Santos, Jose Renato G
2007-Jan-17 00:36 UTC
[Xen-devel] [PATCH] Add RCU support into Xen - Repost
This is a repost of the RCU patch I have posted some time ago.
The only change from the previous post, was to move it to a more
recent version of xen-unstable (changeset 13386).
I am planning to submit the following additional patches, after this
one is accepted:
1) rename_find_domain.patch: Rename find_domain_by_id() to
get_domain_by_id()
2) add_find_domain.patch: Add new find_domain_by_id() function that
uses RCU
3) use_find_domain.patch: Replace invocations of
get_domain_by_id()/put_domain() by find_domain_by_id() where possible.
Thanks
Renato
Patch description: Import linux RCU code into Xen
This is simplified version of the linux code, removing several
components not needed in Xen (at least for now)
================================================================================
Signed-off-by: Jose Renato Santos <jsantos@hpl.hp.com>
# HG changeset patch
# User jsantos@hpl.hp.com
# Date 1168985856 28800
# Node ID fa213888aa931037f33e0b839d324bdee11d43af
# Parent 895d873a00b47cb7b0edf3d0b6a42f47a3f4854c
Add RCU support to Xen
diff -r 895d873a00b4 -r fa213888aa93 xen/arch/x86/setup.c
--- a/xen/arch/x86/setup.c Tue Jan 16 10:02:50 2007 +0000
+++ b/xen/arch/x86/setup.c Tue Jan 16 14:17:36 2007 -0800
@@ -17,6 +17,7 @@
#include <xen/hypercall.h>
#include <xen/keyhandler.h>
#include <xen/numa.h>
+#include <xen/rcupdate.h>
#include <public/version.h>
#ifdef CONFIG_COMPAT
#include <compat/platform.h>
@@ -658,6 +659,8 @@ void __init __start_xen(multiboot_info_t
trap_init();
+ rcu_init();
+
timer_init();
early_time_init();
@@ -693,8 +696,10 @@ void __init __start_xen(multiboot_info_t
{
if ( num_online_cpus() >= max_cpus )
break;
- if ( !cpu_online(i) )
+ if ( !cpu_online(i) ) {
+ rcu_online_cpu(i);
__cpu_up(i);
+ }
/* Set up cpu_to_node[]. */
srat_detect_node(i);
diff -r 895d873a00b4 -r fa213888aa93 xen/common/Makefile
--- a/xen/common/Makefile Tue Jan 16 10:02:50 2007 +0000
+++ b/xen/common/Makefile Tue Jan 16 14:17:36 2007 -0800
@@ -28,6 +28,7 @@ obj-y += version.o
obj-y += version.o
obj-y += vsprintf.o
obj-y += xmalloc.o
+obj-y += rcupdate.o
obj-$(perfc) += perfc.o
obj-$(crash_debug) += gdbstub.o
diff -r 895d873a00b4 -r fa213888aa93 xen/common/rcupdate.c
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/xen/common/rcupdate.c Tue Jan 16 14:17:36 2007 -0800
@@ -0,0 +1,381 @@
+/*
+ * Read-Copy Update mechanism for mutual exclusion
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
02111-1307, USA.
+ *
+ * Copyright (C) IBM Corporation, 2001
+ *
+ * Authors: Dipankar Sarma <dipankar@in.ibm.com>
+ * Manfred Spraul <manfred@colorfullife.com>
+ *
+ * Modifications for Xen: Jose Renato Santos
+ * Copyright (C) Hewlett-Packard, 2006
+ *
+ * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
+ * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
+ * Papers:
+ * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
+ * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf
(OLS2001)
+ *
+ * For detailed explanation of Read-Copy Update mechanism see -
+ * http://lse.sourceforge.net/locking/rcupdate.html
+ *
+ */
+#include <xen/types.h>
+#include <xen/kernel.h>
+#include <xen/init.h>
+#include <xen/spinlock.h>
+#include <xen/smp.h>
+#include <xen/rcupdate.h>
+#include <xen/sched.h>
+#include <asm/atomic.h>
+#include <xen/bitops.h>
+#include <xen/percpu.h>
+#include <xen/softirq.h>
+
+/* Definition for rcupdate control block. */
+struct rcu_ctrlblk rcu_ctrlblk = {
+ .cur = -300,
+ .completed = -300,
+ .lock = SPIN_LOCK_UNLOCKED,
+ .cpumask = CPU_MASK_NONE,
+};
+
+DEFINE_PER_CPU(struct rcu_data, rcu_data) = { 0L };
+
+static int blimit = 10;
+static int qhimark = 10000;
+static int qlowmark = 100;
+#ifdef CONFIG_SMP
+static int rsinterval = 1000;
+#endif
+
+#ifdef CONFIG_SMP
+static void force_quiescent_state(struct rcu_data *rdp,
+ struct rcu_ctrlblk *rcp)
+{
+ cpumask_t cpumask;
+ raise_softirq(SCHEDULE_SOFTIRQ);
+ if (unlikely(rdp->qlen - rdp->last_rs_qlen > rsinterval)) {
+ rdp->last_rs_qlen = rdp->qlen;
+ /*
+ * Don''t send IPI to itself. With irqs disabled,
+ * rdp->cpu is the current cpu.
+ */
+ cpumask = rcp->cpumask;
+ cpu_clear(rdp->cpu, cpumask);
+ cpumask_raise_softirq(cpumask, SCHEDULE_SOFTIRQ);
+ }
+}
+#else
+static inline void force_quiescent_state(struct rcu_data *rdp,
+ struct rcu_ctrlblk *rcp)
+{
+ raise_softirq(SCHEDULE_SOFTIRQ);
+}
+#endif
+
+/**
+ * call_rcu - Queue an RCU callback for invocation after a grace
period.
+ * @head: structure to be used for queueing the RCU updates.
+ * @func: actual update function to be invoked after the grace period
+ *
+ * The update function will be invoked some time after a full grace
+ * period elapses, in other words after all currently executing RCU
+ * read-side critical sections have completed. RCU read-side critical
+ * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
+ * and may be nested.
+ */
+void fastcall call_rcu(struct rcu_head *head,
+ void (*func)(struct rcu_head *rcu))
+{
+ unsigned long flags;
+ struct rcu_data *rdp;
+
+ head->func = func;
+ head->next = NULL;
+ local_irq_save(flags);
+ rdp = &__get_cpu_var(rcu_data);
+ *rdp->nxttail = head;
+ rdp->nxttail = &head->next;
+ /* This should be very unlikely in Xen */
+ if (unlikely(++rdp->qlen > qhimark)) {
+ rdp->blimit = INT_MAX;
+ force_quiescent_state(rdp, &rcu_ctrlblk);
+ }
+ local_irq_restore(flags);
+}
+
+/*
+ * Return the number of RCU batches processed thus far. Useful
+ * for debug and statistics.
+ */
+long rcu_batches_completed(void)
+{
+ return rcu_ctrlblk.completed;
+}
+
+/*
+ * Invoke the completed RCU callbacks. They are expected to be in
+ * a per-cpu list.
+ */
+static void rcu_do_batch(struct rcu_data *rdp)
+{
+ struct rcu_head *next, *list;
+ int count = 0;
+
+ list = rdp->donelist;
+ while (list) {
+ next = rdp->donelist = list->next;
+ list->func(list);
+ list = next;
+ rdp->qlen--;
+ if (++count >= rdp->blimit)
+ break;
+ }
+ if (rdp->blimit == INT_MAX && rdp->qlen <= qlowmark)
+ rdp->blimit = blimit;
+ if (!rdp->donelist)
+ rdp->donetail = &rdp->donelist;
+ else
+ raise_softirq(RCU_SOFTIRQ);
+}
+
+/*
+ * Grace period handling:
+ * The grace period handling consists out of two steps:
+ * - A new grace period is started.
+ * This is done by rcu_start_batch. The start is not broadcasted to
+ * all cpus, they must pick this up by comparing rcp->cur with
+ * rdp->quiescbatch. All cpus are recorded in the
+ * rcu_ctrlblk.cpumask bitmap.
+ * - All cpus must go through a quiescent state.
+ * Since the start of the grace period is not broadcasted, at least
two
+ * calls to rcu_check_quiescent_state are required:
+ * The first call just notices that a new grace period is running.
The
+ * following calls check if there was a quiescent state since the
beginning
+ * of the grace period. If so, it updates rcu_ctrlblk.cpumask. If
+ * the bitmap is empty, then the grace period is completed.
+ * rcu_check_quiescent_state calls rcu_start_batch(0) to start the
next grace
+ * period (if necessary).
+ */
+/*
+ * Register a new batch of callbacks, and start it up if there is
currently no
+ * active batch and the batch to be registered has not already
occurred.
+ * Caller must hold rcu_ctrlblk.lock.
+ */
+static void rcu_start_batch(struct rcu_ctrlblk *rcp)
+{
+ if (rcp->next_pending &&
+ rcp->completed == rcp->cur) {
+ rcp->next_pending = 0;
+ /*
+ * next_pending == 0 must be visible in
+ * __rcu_process_callbacks() before it can see new value
of cur.
+ */
+ smp_wmb();
+ rcp->cur++;
+
+ rcp->cpumask = cpu_online_map;
+ }
+}
+
+/*
+ * cpu went through a quiescent state since the beginning of the grace
period.
+ * Clear it from the cpu mask and complete the grace period if it was
the last
+ * cpu. Start another grace period if someone has further entries
pending
+ */
+static void cpu_quiet(int cpu, struct rcu_ctrlblk *rcp)
+{
+ cpu_clear(cpu, rcp->cpumask);
+ if (cpus_empty(rcp->cpumask)) {
+ /* batch completed ! */
+ rcp->completed = rcp->cur;
+ rcu_start_batch(rcp);
+ }
+}
+
+/*
+ * Check if the cpu has gone through a quiescent state (say context
+ * switch). If so and if it already hasn''t done so in this RCU
+ * quiescent cycle, then indicate that it has done so.
+ */
+static void rcu_check_quiescent_state(struct rcu_ctrlblk *rcp,
+ struct rcu_data *rdp)
+{
+ if (rdp->quiescbatch != rcp->cur) {
+ /* start new grace period: */
+ rdp->qs_pending = 1;
+ rdp->passed_quiesc = 0;
+ rdp->quiescbatch = rcp->cur;
+ return;
+ }
+
+ /* Grace period already completed for this cpu?
+ * qs_pending is checked instead of the actual bitmap to avoid
+ * cacheline trashing.
+ */
+ if (!rdp->qs_pending)
+ return;
+
+ /*
+ * Was there a quiescent state since the beginning of the grace
+ * period? If no, then exit and wait for the next call.
+ */
+ if (!rdp->passed_quiesc)
+ return;
+ rdp->qs_pending = 0;
+
+ spin_lock(&rcp->lock);
+ /*
+ * rdp->quiescbatch/rcp->cur and the cpu bitmap can come out of
sync
+ * during cpu startup. Ignore the quiescent state.
+ */
+ if (likely(rdp->quiescbatch == rcp->cur))
+ cpu_quiet(rdp->cpu, rcp);
+
+ spin_unlock(&rcp->lock);
+}
+
+
+/*
+ * This does the RCU processing work from softirq context.
+ */
+static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp,
+ struct rcu_data *rdp)
+{
+ if (rdp->curlist && !rcu_batch_before(rcp->completed,
rdp->batch)) {
+ *rdp->donetail = rdp->curlist;
+ rdp->donetail = rdp->curtail;
+ rdp->curlist = NULL;
+ rdp->curtail = &rdp->curlist;
+ }
+
+ local_irq_disable();
+ if (rdp->nxtlist && !rdp->curlist) {
+ rdp->curlist = rdp->nxtlist;
+ rdp->curtail = rdp->nxttail;
+ rdp->nxtlist = NULL;
+ rdp->nxttail = &rdp->nxtlist;
+ local_irq_enable();
+
+ /*
+ * start the next batch of callbacks
+ */
+
+ /* determine batch number */
+ rdp->batch = rcp->cur + 1;
+ /* see the comment and corresponding wmb() in
+ * the rcu_start_batch()
+ */
+ smp_rmb();
+
+ if (!rcp->next_pending) {
+ /* and start it/schedule start if it''s a new
batch */
+ spin_lock(&rcp->lock);
+ rcp->next_pending = 1;
+ rcu_start_batch(rcp);
+ spin_unlock(&rcp->lock);
+ }
+ } else {
+ local_irq_enable();
+ }
+ rcu_check_quiescent_state(rcp, rdp);
+ if (rdp->donelist)
+ rcu_do_batch(rdp);
+}
+
+static void rcu_process_callbacks(void)
+{
+ __rcu_process_callbacks(&rcu_ctrlblk, &__get_cpu_var(rcu_data));
+}
+
+static int __rcu_pending(struct rcu_ctrlblk *rcp, struct rcu_data *rdp)
+{
+ /* This cpu has pending rcu entries and the grace period
+ * for them has completed.
+ */
+ if (rdp->curlist && !rcu_batch_before(rcp->completed,
rdp->batch))
+ return 1;
+
+ /* This cpu has no pending entries, but there are new entries */
+ if (!rdp->curlist && rdp->nxtlist)
+ return 1;
+
+ /* This cpu has finished callbacks to invoke */
+ if (rdp->donelist)
+ return 1;
+
+ /* The rcu core waits for a quiescent state from the cpu */
+ if (rdp->quiescbatch != rcp->cur || rdp->qs_pending)
+ return 1;
+
+ /* nothing to do */
+ return 0;
+}
+
+int rcu_pending(int cpu)
+{
+ return __rcu_pending(&rcu_ctrlblk, &per_cpu(rcu_data, cpu));
+}
+
+/*
+ * Check to see if any future RCU-related work will need to be done
+ * by the current CPU, even if none need be done immediately, returning
+ * 1 if so. This function is part of the RCU implementation; it is
-not-
+ * an exported member of the RCU API.
+ */
+int rcu_needs_cpu(int cpu)
+{
+ struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
+
+ return (!!rdp->curlist || rcu_pending(cpu));
+}
+
+void rcu_check_callbacks(int cpu, int qstate)
+{
+ if (qstate) {
+ rcu_qsctr_inc(cpu);
+ }
+ raise_softirq(RCU_SOFTIRQ);
+}
+
+static void rcu_init_percpu_data(int cpu, struct rcu_ctrlblk *rcp,
+ struct rcu_data *rdp)
+{
+ memset(rdp, 0, sizeof(*rdp));
+ rdp->curtail = &rdp->curlist;
+ rdp->nxttail = &rdp->nxtlist;
+ rdp->donetail = &rdp->donelist;
+ rdp->quiescbatch = rcp->completed;
+ rdp->qs_pending = 0;
+ rdp->cpu = cpu;
+ rdp->blimit = blimit;
+}
+
+void __devinit rcu_online_cpu(int cpu)
+{
+ struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
+
+ rcu_init_percpu_data(cpu, &rcu_ctrlblk, rdp);
+}
+
+void rcu_init(void)
+{
+ rcu_online_cpu(smp_processor_id());
+ open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
+}
+
+
diff -r 895d873a00b4 -r fa213888aa93 xen/common/schedule.c
--- a/xen/common/schedule.c Tue Jan 16 10:02:50 2007 +0000
+++ b/xen/common/schedule.c Tue Jan 16 14:17:36 2007 -0800
@@ -30,6 +30,7 @@
#include <xen/mm.h>
#include <xen/errno.h>
#include <xen/guest_access.h>
+#include <xen/rcupdate.h>
#include <xen/multicall.h>
#include <public/sched.h>
@@ -552,9 +553,15 @@ static void schedule(void)
struct schedule_data *sd;
struct task_slice next_slice;
s32 r_time; /* time for new dom to run */
+ int cpu = smp_processor_id();
ASSERT(!in_irq());
ASSERT(this_cpu(mc_state).flags == 0);
+
+ if (rcu_pending(cpu))
+ /* since __enter_scheduler is called from softirq context
+ * we know we are in a quiescent state */
+ rcu_check_callbacks(cpu,1);
perfc_incrc(sched_run);
@@ -649,6 +656,12 @@ static void t_timer_fn(void *unused)
static void t_timer_fn(void *unused)
{
struct vcpu *v = current;
+ int cpu = smp_processor_id();
+
+ if (rcu_pending(cpu))
+ /* since t_timer_fn is called from softirq context
+ * we know we are in a quiescent state */
+ rcu_check_callbacks(cpu,1);
this_cpu(schedule_data).tick++;
diff -r 895d873a00b4 -r fa213888aa93 xen/include/xen/rcupdate.h
--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/xen/include/xen/rcupdate.h Tue Jan 16 14:17:36 2007 -0800
@@ -0,0 +1,213 @@
+/*
+ * Read-Copy Update mechanism for mutual exclusion
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
02111-1307, USA.
+ *
+ * Copyright (C) IBM Corporation, 2001
+ *
+ * Author: Dipankar Sarma <dipankar@in.ibm.com>
+ *
+ * Based on the original work by Paul McKenney
<paul.mckenney@us.ibm.com>
+ * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
+ * Papers:
+ * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
+ * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf
(OLS2001)
+ *
+ * For detailed explanation of Read-Copy Update mechanism see -
+ * http://lse.sourceforge.net/locking/rcupdate.html
+ *
+ */
+
+#ifndef __XEN_RCUPDATE_H
+#define __XEN_RCUPDATE_H
+
+#include <xen/cache.h>
+#include <xen/spinlock.h>
+#include <xen/percpu.h>
+#include <xen/cpumask.h>
+
+/**
+ * struct rcu_head - callback structure for use with RCU
+ * @next: next update requests in a list
+ * @func: actual update function to call after the grace period.
+ */
+struct rcu_head {
+ struct rcu_head *next;
+ void (*func)(struct rcu_head *head);
+};
+
+#define RCU_HEAD_INIT { .next = NULL, .func = NULL }
+#define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT
+#define INIT_RCU_HEAD(ptr) do { \
+ (ptr)->next = NULL; (ptr)->func = NULL; \
+} while (0)
+
+
+
+/* Global control variables for rcupdate callback mechanism. */
+struct rcu_ctrlblk {
+ long cur; /* Current batch number.
*/
+ long completed; /* Number of the last completed batch
*/
+ int next_pending; /* Is the next batch already waiting?
*/
+
+ spinlock_t lock __cacheline_aligned;
+ cpumask_t cpumask; /* CPUs that need to switch in order
*/
+ /* for current batch to proceed.
*/
+} __cacheline_aligned;
+
+/* Is batch a before batch b ? */
+static inline int rcu_batch_before(long a, long b)
+{
+ return (a - b) < 0;
+}
+
+/* Is batch a after batch b ? */
+static inline int rcu_batch_after(long a, long b)
+{
+ return (a - b) > 0;
+}
+
+/*
+ * Per-CPU data for Read-Copy UPdate.
+ * nxtlist - new callbacks are added here
+ * curlist - current batch for which quiescent cycle started if any
+ */
+struct rcu_data {
+ /* 1) quiescent state handling : */
+ long quiescbatch; /* Batch # for grace period */
+ int passed_quiesc; /* User-mode/idle loop etc. */
+ int qs_pending; /* core waits for quiesc state
*/
+
+ /* 2) batch handling */
+ long batch; /* Batch # for current RCU
batch */
+ struct rcu_head *nxtlist;
+ struct rcu_head **nxttail;
+ long qlen; /* # of queued callbacks */
+ struct rcu_head *curlist;
+ struct rcu_head **curtail;
+ struct rcu_head *donelist;
+ struct rcu_head **donetail;
+ long blimit; /* Upper limit on a processed
batch */
+ int cpu;
+ struct rcu_head barrier;
+#ifdef CONFIG_SMP
+ long last_rs_qlen; /* qlen during the last resched
*/
+#endif
+};
+
+DECLARE_PER_CPU(struct rcu_data, rcu_data);
+extern struct rcu_ctrlblk rcu_ctrlblk;
+
+/*
+ * Increment the quiescent state counter.
+ * The counter is a bit degenerated: We do not need to know
+ * how many quiescent states passed, just if there was at least
+ * one since the start of the grace period. Thus just a flag.
+ */
+static inline void rcu_qsctr_inc(int cpu)
+{
+ struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
+ rdp->passed_quiesc = 1;
+}
+
+extern int rcu_pending(int cpu);
+extern int rcu_needs_cpu(int cpu);
+
+/**
+ * rcu_read_lock - mark the beginning of an RCU read-side critical
section.
+ *
+ * When call_rcu() is invoked
+ * on one CPU while other CPUs are within RCU read-side critical
+ * sections, invocation of the corresponding RCU callback is deferred
+ * until after the all the other CPUs exit their critical sections.
+ *
+ * Note, however, that RCU callbacks are permitted to run concurrently
+ * with RCU read-side critical sections. One way that this can happen
+ * is via the following sequence of events: (1) CPU 0 enters an RCU
+ * read-side critical section, (2) CPU 1 invokes call_rcu() to register
+ * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
+ * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
+ * callback is invoked. This is legal, because the RCU read-side
critical
+ * section that was running concurrently with the call_rcu() (and which
+ * therefore might be referencing something that the corresponding RCU
+ * callback would free up) has completed before the corresponding
+ * RCU callback is invoked.
+ *
+ * RCU read-side critical sections may be nested. Any deferred actions
+ * will be deferred until the outermost RCU read-side critical section
+ * completes.
+ *
+ * It is illegal to block while in an RCU read-side critical section.
+ */
+#define rcu_read_lock() do { } while (0)
+
+/**
+ * rcu_read_unlock - marks the end of an RCU read-side critical
section.
+ *
+ * See rcu_read_lock() for more information.
+ */
+#define rcu_read_unlock() do { } while (0)
+
+/*
+ * So where is rcu_write_lock()? It does not exist, as there is no
+ * way for writers to lock out RCU readers. This is a feature, not
+ * a bug -- this property is what provides RCU''s performance benefits.
+ * Of course, writers must coordinate with each other. The normal
+ * spinlock primitives work well for this, but any other technique may
be
+ * used as well. RCU does not care how the writers keep out of each
+ * others'' way, as long as they do so.
+ */
+
+/**
+ * rcu_dereference - fetch an RCU-protected pointer in an
+ * RCU read-side critical section. This pointer may later
+ * be safely dereferenced.
+ *
+ * Inserts memory barriers on architectures that require them
+ * (currently only the Alpha), and, more importantly, documents
+ * exactly which pointers are protected by RCU.
+ */
+
+/* As Xen does not run on alpha this is a no op */
+#define rcu_dereference(p) (p)
+
+/**
+ * rcu_assign_pointer - assign (publicize) a pointer to a newly
+ * initialized structure that will be dereferenced by RCU read-side
+ * critical sections. Returns the value assigned.
+ *
+ * Inserts memory barriers on architectures that require them
+ * (pretty much all of them other than x86), and also prevents
+ * the compiler from reordering the code that initializes the
+ * structure after the pointer assignment. More importantly, this
+ * call documents which pointers will be dereferenced by RCU read-side
+ * code.
+ */
+
+#define rcu_assign_pointer(p, v) ({ \
+ smp_wmb(); \
+ (p) = (v); \
+ })
+
+extern void rcu_init(void);
+extern void __devinit rcu_online_cpu(int cpu);
+extern void rcu_check_callbacks(int cpu, int qstate);
+extern long rcu_batches_completed(void);
+
+/* Exported interfaces */
+extern void fastcall call_rcu(struct rcu_head *head,
+ void (*func)(struct rcu_head *head));
+
+#endif /* __XEN_RCUPDATE_H */
diff -r 895d873a00b4 -r fa213888aa93 xen/include/xen/softirq.h
--- a/xen/include/xen/softirq.h Tue Jan 16 10:02:50 2007 +0000
+++ b/xen/include/xen/softirq.h Tue Jan 16 14:17:36 2007 -0800
@@ -9,8 +9,9 @@
#define NMI_SOFTIRQ 4
#define PAGE_SCRUB_SOFTIRQ 5
#define TRACE_SOFTIRQ 6
+#define RCU_SOFTIRQ 7
-#define NR_COMMON_SOFTIRQS 7
+#define NR_COMMON_SOFTIRQS 8
#include <asm/softirq.h>
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xensource.com
http://lists.xensource.com/xen-devel
Keir Fraser
2007-Jan-26 18:40 UTC
Re: [Xen-devel] [PATCH] Add RCU support into Xen - Repost
On 17/1/07 12:36 am, "Santos, Jose Renato G" <joserenato.santos@hp.com> wrote:> I am planning to submit the following additional patches, after this > one is accepted:Now done. C/s 13648. I ripped out a few more bits of the Linux RCU implementation and moved the hooks in schedule.c to a single hook in do_softirq(). I suspect there is a tradeoff between timeliness of checking for pending work and building up nice batches of RCU work but checking in do_softirq() shouldn''t mean we''re hitting the RCU variables too often.> 1) rename_find_domain.patch: Rename find_domain_by_id() to > get_domain_by_id()Also done, by sed. C/s 13649. -- Keir> 2) add_find_domain.patch: Add new find_domain_by_id() function that > uses RCU > 3) use_find_domain.patch: Replace invocations of > get_domain_by_id()/put_domain() by find_domain_by_id() where possible._______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Santos, Jose Renato G
2007-Jan-30 19:05 UTC
RE: [Xen-devel] [PATCH] Add RCU support into Xen - Repost
> -----Original Message----- > From: Keir Fraser [mailto:Keir.Fraser@cl.cam.ac.uk] > Sent: Friday, January 26, 2007 10:40 AM > To: Santos, Jose Renato G; xen-devel@lists.xensource.com > Cc: Turner, Yoshio; Jose Renato Santos; G John Janakiraman > Subject: Re: [Xen-devel] [PATCH] Add RCU support into Xen - Repost > > On 17/1/07 12:36 am, "Santos, Jose Renato G" > <joserenato.santos@hp.com> > wrote: > > > I am planning to submit the following additional patches, > after this > > one is accepted: > > Now done. C/s 13648. I ripped out a few more bits of the > Linux RCU implementation and moved the hooks in schedule.c to > a single hook in do_softirq(). I suspect there is a tradeoff > between timeliness of checking for pending work and building > up nice batches of RCU work but checking in > do_softirq() shouldn''t mean we''re hitting the RCU variables too often. >Yes, that should be fine. The overhead should be small if we are only checking if there is RCU work to do. Looking at your changes, I think there are a few more bits that we can remove of the Linux RCU implementation. I will prepare a patch for you with some cleanup later. But, for now I would like to focus on the patches that modify the domain list manipulation and find_domain_by_id()to use the new RCU functions. While doing that I noticed that you removed the definitions of "rcu_read_lock()" and "rcu_read_unlock()" from rcupdate.h. Although they are really NOPs I think it would be good if we use them in all RCU read critical sections, for code clarity and documentation (as linux does). Can we add those back? Thanks Renato> > 1) rename_find_domain.patch: Rename find_domain_by_id() to > > get_domain_by_id() > > Also done, by sed. C/s 13649. > > -- Keir > > > 2) add_find_domain.patch: Add new find_domain_by_id() function > > that uses RCU > > 3) use_find_domain.patch: Replace invocations of > > get_domain_by_id()/put_domain() by find_domain_by_id() > where possible. > > >_______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Keir Fraser
2007-Jan-30 20:23 UTC
Re: [Xen-devel] [PATCH] Add RCU support into Xen - Repost
On 30/1/07 7:05 pm, "Santos, Jose Renato G" <joserenato.santos@hp.com> wrote:> While doing that I noticed that you removed the definitions of > "rcu_read_lock()" and "rcu_read_unlock()" from rcupdate.h. > Although they are really NOPs I think it would be good if we use > them in all RCU read critical sections, for code clarity > and documentation (as linux does). > Can we add those back?This would require some interaction with new find_domain_by_id(). The invocation of find_domain_by_id() and all subsequent uses of its return value will need to be contained within an rcu_read_lock()/rcu_read_unlock() pair which seems kind of a pain. Particularly since this documentation is weak -- it may not immediately be clear in future what is being protected by the rcu read-side region (since the lock routines do not take a parameter). And I''m not sure how the documentation helps: who will it be useful to? Linux needs them for more than just documentation as it has to disable preemption (a feature which I don''t expect Xen to ever acquire). I don''t know whether it would have them otherwise. -- Keir _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Keir Fraser
2007-Jan-30 20:37 UTC
Re: [Xen-devel] [PATCH] Add RCU support into Xen - Repost
On 30/1/07 8:23 pm, "Keir Fraser" <Keir.Fraser@cl.cam.ac.uk> wrote:> This would require some interaction with new find_domain_by_id(). The > invocation of find_domain_by_id() and all subsequent uses of its return > value will need to be contained within an rcu_read_lock()/rcu_read_unlock() > pair which seems kind of a pain. Particularly since this documentation is > weak -- it may not immediately be clear in future what is being protected by > the rcu read-side region (since the lock routines do not take a parameter). > And I''m not sure how the documentation helps: who will it be useful to?Thinking about this a little more, we could wrap up the rcu_read_[un]lock invocations into a more informative API in this case: get_domain_by_id_rcu(d) and put_domain_rcu(d), analagous with get_domain/put_domain. get_domain_by_rcu(d) would include an implicit rcu_read_lock(), and put_domain_rcu(d) an implicit rcu_read_unlock(). I could certainly live with that, and then keep direct use of rcu_read_lock()/rcu_read_unlock() for small critical regions (e.g., in the implementation of get_domain_by_id()). -- Keir> Linux needs them for more than just documentation as it has to disable > preemption (a feature which I don''t expect Xen to ever acquire). I don''t > know whether it would have them otherwise. > > -- Keir > > > > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xensource.com > http://lists.xensource.com/xen-devel_______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Santos, Jose Renato G
2007-Jan-30 22:46 UTC
RE: [Xen-devel] [PATCH] Add RCU support into Xen - Repost
> -----Original Message----- > From: Keir Fraser [mailto:Keir.Fraser@cl.cam.ac.uk] > Sent: Tuesday, January 30, 2007 12:37 PM > To: Keir Fraser; Santos, Jose Renato G; xen-devel@lists.xensource.com > Cc: Turner, Yoshio; Jose Renato Santos; G John Janakiraman > Subject: Re: [Xen-devel] [PATCH] Add RCU support into Xen - Repost > > On 30/1/07 8:23 pm, "Keir Fraser" <Keir.Fraser@cl.cam.ac.uk> wrote: > > > This would require some interaction with new > find_domain_by_id(). The > > invocation of find_domain_by_id() and all subsequent uses of its > > return value will need to be contained within an > > rcu_read_lock()/rcu_read_unlock() pair which seems kind of a pain. > > Particularly since this documentation is weak -- it may not > > immediately be clear in future what is being protected by > the rcu read-side region (since the lock routines do not take > a parameter). > > And I''m not sure how the documentation helps: who will it > be useful to? > > Thinking about this a little more, we could wrap up the > rcu_read_[un]lock invocations into a more informative API in > this case: > get_domain_by_id_rcu(d) and put_domain_rcu(d), analagous with > get_domain/put_domain. get_domain_by_rcu(d) would include an > implicit rcu_read_lock(), and put_domain_rcu(d) an implicit > rcu_read_unlock(). >That is a good idea, although I would prefer if we could find better names for the rcu functions. Get/put may give the wrong impression that a reference counter is being incremented/decremented which would not be the case. It could also give the wrong impression that the matching "put" could be invoked any time later which may leave us with an invalid domain pointer (if the pointer is kept beyond the current Xen invocation). What about "find_domain_rcu()"/"end_find_domain_rcu()" ? Renato> I could certainly live with that, and then keep direct use of > rcu_read_lock()/rcu_read_unlock() for small critical regions > (e.g., in the implementation of get_domain_by_id()). > > -- Keir > > > Linux needs them for more than just documentation as it has > to disable > > preemption (a feature which I don''t expect Xen to ever acquire). I > > don''t know whether it would have them otherwise. > > > > -- Keir > > > > > > > > _______________________________________________ > > Xen-devel mailing list > > Xen-devel@lists.xensource.com > > http://lists.xensource.com/xen-devel > > >_______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Santos, Jose Renato G
2007-Jan-31 23:52 UTC
RE: [Xen-devel] [PATCH] Add RCU support into Xen - Repost
Keir The attached patch changes all accesses to domain_list and domain_hash to use RCU. I have also included a patch restoring the definition of rcu_read_lock() and rcu_read_unlock() back to rcupdate.h, since these are used on the patch. I think you have agreed to have those back according to your last email. These patches apply cleanly to c/s 13703. Thanks Renato> -----Original Message----- > From: Santos, Jose Renato G > Sent: Tuesday, January 30, 2007 2:46 PM > To: Keir Fraser; xen-devel@lists.xensource.com > Cc: Turner, Yoshio; Jose Renato Santos; G John Janakiraman > Subject: RE: [Xen-devel] [PATCH] Add RCU support into Xen - Repost > > > > > -----Original Message----- > > From: Keir Fraser [mailto:Keir.Fraser@cl.cam.ac.uk] > > Sent: Tuesday, January 30, 2007 12:37 PM > > To: Keir Fraser; Santos, Jose Renato G; > xen-devel@lists.xensource.com > > Cc: Turner, Yoshio; Jose Renato Santos; G John Janakiraman > > Subject: Re: [Xen-devel] [PATCH] Add RCU support into Xen - Repost > > > > On 30/1/07 8:23 pm, "Keir Fraser" <Keir.Fraser@cl.cam.ac.uk> wrote: > > > > > This would require some interaction with new > > find_domain_by_id(). The > > > invocation of find_domain_by_id() and all subsequent uses of its > > > return value will need to be contained within an > > > rcu_read_lock()/rcu_read_unlock() pair which seems kind > of a pain. > > > Particularly since this documentation is weak -- it may not > > > immediately be clear in future what is being protected by > > the rcu read-side region (since the lock routines do not take a > > parameter). > > > And I''m not sure how the documentation helps: who will it > > be useful to? > > > > Thinking about this a little more, we could wrap up the > > rcu_read_[un]lock invocations into a more informative API in this > > case: > > get_domain_by_id_rcu(d) and put_domain_rcu(d), analagous with > > get_domain/put_domain. get_domain_by_rcu(d) would include > an implicit > > rcu_read_lock(), and put_domain_rcu(d) an implicit > rcu_read_unlock(). > > > > That is a good idea, although I would prefer if we could > find better names for the rcu functions. Get/put may give the > wrong impression that a reference counter is being > incremented/decremented which would not be the case. It could > also give the wrong impression that the matching "put" could > be invoked any time later which may leave us with an invalid > domain pointer (if the pointer is kept beyond the current Xen > invocation). What about "find_domain_rcu()"/"end_find_domain_rcu()" ? > > Renato > > > > > I could certainly live with that, and then keep direct use of > > rcu_read_lock()/rcu_read_unlock() for small critical > regions (e.g., in > > the implementation of get_domain_by_id()). > > > > -- Keir > > > > > Linux needs them for more than just documentation as it has > > to disable > > > preemption (a feature which I don''t expect Xen to ever > acquire). I > > > don''t know whether it would have them otherwise. > > > > > > -- Keir > > > > > > > > > > > > _______________________________________________ > > > Xen-devel mailing list > > > Xen-devel@lists.xensource.com > > > http://lists.xensource.com/xen-devel > > > > > > >_______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Keir Fraser
2007-Feb-01 18:01 UTC
Re: [Xen-devel] [PATCH] Add RCU support into Xen - Repost
On 30/1/07 22:46, "Santos, Jose Renato G" <joserenato.santos@hp.com> wrote:> That is a good idea, although I would prefer if we could find > better names for the rcu functions. Get/put may give the wrong > impression that a reference counter is being incremented/decremented > which would not be the case. It could also give the wrong impression > that the matching "put" could be invoked any time later which may > leave us with an invalid domain pointer (if the pointer is kept > beyond the current Xen invocation). What about > "find_domain_rcu()"/"end_find_domain_rcu()" ?Find_domain_by_id_rcu()/end_domain_rcu()? -- Keir _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Santos, Jose Renato G
2007-Feb-01 20:16 UTC
RE: [Xen-devel] [PATCH] Add RCU support into Xen - Repost
> -----Original Message----- > From: Keir Fraser [mailto:Keir.Fraser@cl.cam.ac.uk] > Sent: Thursday, February 01, 2007 10:02 AM > To: Santos, Jose Renato G; xen-devel@lists.xensource.com > Cc: Turner, Yoshio; Jose Renato Santos; G John Janakiraman > Subject: Re: [Xen-devel] [PATCH] Add RCU support into Xen - Repost > > On 30/1/07 22:46, "Santos, Jose Renato G" > <joserenato.santos@hp.com> wrote: > > > That is a good idea, although I would prefer if we could > find better > > names for the rcu functions. Get/put may give the wrong impression > > that a reference counter is being incremented/decremented > which would > > not be the case. It could also give the wrong impression that the > > matching "put" could be invoked any time later which may > leave us with > > an invalid domain pointer (if the pointer is kept beyond > the current > > Xen invocation). What about > > "find_domain_rcu()"/"end_find_domain_rcu()" ? > > Find_domain_by_id_rcu()/end_domain_rcu()? >Do we really need to have "by_id" on the name? Isn''t find_domain_rcu() clear enough? After all, from the function definition it should be clear that it takes a domid as parameter. I like end_domain_rcu(). Renato> -- Keir > > >_______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Santos, Jose Renato G
2007-Feb-01 21:25 UTC
RE: [Xen-devel] [PATCH] Add RCU support into Xen - Repost
> -----Original Message----- > From: Santos, Jose Renato G > Sent: Thursday, February 01, 2007 12:16 PM > To: Keir Fraser; xen-devel@lists.xensource.com > Cc: Turner, Yoshio; Jose Renato Santos; G John Janakiraman > Subject: RE: [Xen-devel] [PATCH] Add RCU support into Xen - Repost > > > > > -----Original Message----- > > From: Keir Fraser [mailto:Keir.Fraser@cl.cam.ac.uk] > > Sent: Thursday, February 01, 2007 10:02 AM > > To: Santos, Jose Renato G; xen-devel@lists.xensource.com > > Cc: Turner, Yoshio; Jose Renato Santos; G John Janakiraman > > Subject: Re: [Xen-devel] [PATCH] Add RCU support into Xen - Repost > > > > On 30/1/07 22:46, "Santos, Jose Renato G" > > <joserenato.santos@hp.com> wrote: > > > > > That is a good idea, although I would prefer if we could > > find better > > > names for the rcu functions. Get/put may give the wrong > impression > > > that a reference counter is being incremented/decremented > > which would > > > not be the case. It could also give the wrong impression that the > > > matching "put" could be invoked any time later which may > > leave us with > > > an invalid domain pointer (if the pointer is kept beyond > > the current > > > Xen invocation). What about > > > "find_domain_rcu()"/"end_find_domain_rcu()" ? > > > > Find_domain_by_id_rcu()/end_domain_rcu()? > > > > Do we really need to have "by_id" on the name? Isn''t > find_domain_rcu() clear enough? > After all, from the function definition it should be clear > that it takes a domid as parameter. > I like end_domain_rcu(). > Renato >Another possibility could be find_domain_rcu_lock()/domain_rcu_unlock() Just pick your favorite and I will go with it Thanks Renato> > -- Keir > > > > > > >_______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Keir Fraser
2007-Feb-01 23:18 UTC
Re: [Xen-devel] [PATCH] Add RCU support into Xen - Repost
On 1/2/07 21:25, "Santos, Jose Renato G" <joserenato.santos@hp.com> wrote:> Another possibility could be > find_domain_rcu_lock()/domain_rcu_unlock() > Just pick your favorite and I will go with it > Thanks > RenatoYeah, I like this a little more than find/end. Let''s go with it. -- Keir _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Liang Yang
2007-Feb-02 18:39 UTC
[Xen-devel] Is CPU overhead really independent of packet size in Xen?
Hi, I''m reading some Xen performance slides which is published on XenSummit (www.xensource.com/files/summit_3/perf-isolation-gupta.pdf). The presenter claims the CPU overhead is independent of network packet size in Xen VM domains. I haven''t done much research on network I/O on Xen, but I have done many experiments on disk I/O. Based on my disk I/O experimental results, I found out, generally the CPU utilization decrease as the I/O packet size increase which is consistent with the IPv4 forwarding experiments I did before (not on Xen, on plain IA32 Linux). The only exception I noticed is DomainUF. For both small size and large size sequential I/O, the CPU utilization in DomainUF remains almost constant (100%) while CPU utilization drops for 4k and 8K random I/O. If anyone in this mailing list has done similar experiments, please adivse the difference when considering CPU utilization for network I/O and disk I/O? or should both network I/O and disk I/O have the same curve of CPU utilization vs. Packet Size? Thanks, Liang _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
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