Rob Gardner
2005-Oct-30 21:14 UTC
[Xen-devel] [PATCH] Changes to allow dynamic enabling/disabling of trace buffers
This is a set of changes which allow the tracebuffer functionality to
be enabled and disabled dynamically while the system is running. The
existing DOM0_TBUFCONTROL hypercall is used, and three new operations
have been added: enable, disable, and set_size. This is to address
concerns that use of the trace buffers impacts system performance.
The initial value of opt_tbuf_size is set to zero, so that trace
buffers remain disabled by default. They can be enabled as they used
to be, by adding tbuf_size= to the xen command line at boot time. They
can also be turned on and off any time when the system is running. The
size of the trace buffer allocation can also be changed dynamically
while the system is running. The trace buffers may be completely
deallocated by setting the size to zero. No change in buffer size can
be done while tracing is enabled;
Other Changes made:
- Update the constants in tools/xentrace/formats to match those in
public/trace.h
- libxc functions for enable/disable, get/set size
Still left to do:
- remove all ifdef''s for trace buffers and the
''trace'' build option
- xm command to do enable/disable trace buffers and get/set size
Signed-off-by: Rob Gardner <rob.gardner@hp.com>
# HG changeset patch
# User rob.gardner@hp.com
# Node ID 63d05000cfa355c0696aa7efea67668c8cae19f0
# Parent e70ea9465b310e1cba9678ac4e9ad534bb8b670a
Changes to allow the tracebuffer functionality to be enabled and
disabled dynamically while the system is running.
diff -r e70ea9465b31 -r 63d05000cfa3 tools/libxc/Makefile
--- a/tools/libxc/Makefile Thu Oct 27 09:53:02 2005
+++ b/tools/libxc/Makefile Sun Oct 30 20:59:45 2005
@@ -23,6 +23,7 @@
SRCS += xc_physdev.c
SRCS += xc_private.c
SRCS += xc_sedf.c
+SRCS += xc_tbuf.c
BUILD_SRCS += xc_linux_build.c
BUILD_SRCS += xc_load_bin.c
BUILD_SRCS += xc_load_elf.c
diff -r e70ea9465b31 -r 63d05000cfa3 tools/libxc/xenctrl.h
--- a/tools/libxc/xenctrl.h Thu Oct 27 09:53:02 2005
+++ b/tools/libxc/xenctrl.h Sun Oct 30 20:59:45 2005
@@ -149,7 +149,7 @@
const char *corename);
/*
- * This function sets the maximum number vcpus that a domian may create.
+ * This function sets the maximum number of vcpus that a domain may create.
*
* @parm xc_handle a handle to an open hypervisor interface.
* @parm domid the domain id in which vcpus are to be created.
@@ -483,6 +483,47 @@
/* Get current total pages allocated to a domain. */
long xc_get_tot_pages(int xc_handle, uint32_t domid);
+
+
+/*
+ * Trace Buffer Operations
+ */
+
+/**
+ * This function enables or disables tracing. Trace buffer memory must
+ * be already allocated by setting the size to a non-zero value, otherwise
+ * tracing cannot be enabled.
+ *
+ * @parm xc_handle a handle to an open hypervisor interface
+ * @parm enable the desired action, 1 for enable, 0 for disable
+ * @return 0 on success, -1 on failure.
+ */
+int xc_tbuf_enable(int xc_handle, int enable);
+
+/**
+ * This function sets the size of the trace buffers. Setting it to zero
+ * deallocates the memory used for trace buffers, and setting it to a
+ * non-zero value specifies the number of pages per cpu to allocate.
+ * To change the size of an existing allocation, you must first deallocate
+ * it then reallocate it. No change in size is allowed when tracing is
+ * enabled; A disable call must be made first.
+ *
+ * @parm xc_handle a handle to an open hypervisor interface
+ * @parm size the size in pages per cpu for the trace buffers
+ * @return 0 on success, -1 on failure.
+ */
+int xc_tbuf_set_size(int xc_handle, uint32_t size);
+
+/**
+ * This function retrieves the current size of the trace buffers.
+ * Note that the size returned is in terms of bytes, not pages.
+
+ * @parm xc_handle a handle to an open hypervisor interface
+ * @parm size will contain the size in bytes for the trace buffers
+ * @return 0 on success, -1 on failure.
+ */
+int xc_tbuf_get_size(int xc_handle, uint32_t *size);
+
/* Execute a privileged dom0 operation. */
int xc_dom0_op(int xc_handle, dom0_op_t *op);
diff -r e70ea9465b31 -r 63d05000cfa3 tools/xentrace/Makefile
--- a/tools/xentrace/Makefile Thu Oct 27 09:53:02 2005
+++ b/tools/xentrace/Makefile Sun Oct 30 20:59:45 2005
@@ -14,7 +14,7 @@
HDRS = $(wildcard *.h)
OBJS = $(patsubst %.c,%.o,$(wildcard *.c))
-BIN = xentrace
+BIN = xentrace tbctl setsize
SCRIPTS = xentrace_format
MAN1 = $(wildcard *.1)
MAN8 = $(wildcard *.8)
diff -r e70ea9465b31 -r 63d05000cfa3 tools/xentrace/formats
--- a/tools/xentrace/formats Thu Oct 27 09:53:02 2005
+++ b/tools/xentrace/formats Sun Oct 30 20:59:45 2005
@@ -1,16 +1,16 @@
-0x00020001 CPU%(cpu)d %(tsc)d sched_add_domain [ domid
= 0x%(1)08x, edomid = 0x%(2)08x ]
-0x00020002 CPU%(cpu)d %(tsc)d sched_rem_domain [ domid
= 0x%(1)08x, edomid = 0x%(2)08x ]
-0x00020003 CPU%(cpu)d %(tsc)d domain_sleep [ domid
= 0x%(1)08x, edomid = 0x%(2)08x ]
-0x00020004 CPU%(cpu)d %(tsc)d domain_wake [ domid =
0x%(1)08x, edomid = 0x%(2)08x ]
-0x00020005 CPU%(cpu)d %(tsc)d do_yield [ domid =
0x%(1)08x, edomid = 0x%(2)08x ]
-0x00020006 CPU%(cpu)d %(tsc)d do_block [ domid =
0x%(1)08x, edomid = 0x%(2)08x ]
-0x00020007 CPU%(cpu)d %(tsc)d domain_shutdown [
domid = 0x%(1)08x, edomid = 0x%(2)08x, reason = 0x%(3)08x ]
-0x00020008 CPU%(cpu)d %(tsc)d sched_ctl
-0x00020009 CPU%(cpu)d %(tsc)d sched_adjdom [ domid
= 0x%(1)08x ]
-0x0002000a CPU%(cpu)d %(tsc)d __enter_scheduler [
prev<domid:edomid> = 0x%(1)08x : 0x%(2)08x, next<domid:edomid> =
0x%(3)08x : 0x%(4)08x ]
-0x0002000B CPU%(cpu)d %(tsc)d s_timer_fn
-0x0002000c CPU%(cpu)d %(tsc)d t_timer_fn
-0x0002000d CPU%(cpu)d %(tsc)d dom_timer_fn
+0x0002f001 CPU%(cpu)d %(tsc)d sched_add_domain [ domid
= 0x%(1)08x, edomid = 0x%(2)08x ]
+0x0002f002 CPU%(cpu)d %(tsc)d sched_rem_domain [ domid
= 0x%(1)08x, edomid = 0x%(2)08x ]
+0x0002f003 CPU%(cpu)d %(tsc)d domain_sleep [ domid
= 0x%(1)08x, edomid = 0x%(2)08x ]
+0x0002f004 CPU%(cpu)d %(tsc)d domain_wake [ domid =
0x%(1)08x, edomid = 0x%(2)08x ]
+0x0002f005 CPU%(cpu)d %(tsc)d do_yield [ domid =
0x%(1)08x, edomid = 0x%(2)08x ]
+0x0002f006 CPU%(cpu)d %(tsc)d do_block [ domid =
0x%(1)08x, edomid = 0x%(2)08x ]
+0x0002f007 CPU%(cpu)d %(tsc)d domain_shutdown [
domid = 0x%(1)08x, edomid = 0x%(2)08x, reason = 0x%(3)08x ]
+0x0002f008 CPU%(cpu)d %(tsc)d sched_ctl
+0x0002f009 CPU%(cpu)d %(tsc)d sched_adjdom [ domid
= 0x%(1)08x ]
+0x0002f00a CPU%(cpu)d %(tsc)d __enter_scheduler [
prev<domid:edomid> = 0x%(1)08x : 0x%(2)08x, next<domid:edomid> =
0x%(3)08x : 0x%(4)08x ]
+0x0002f00B CPU%(cpu)d %(tsc)d s_timer_fn
+0x0002f00c CPU%(cpu)d %(tsc)d t_timer_fn
+0x0002f00d CPU%(cpu)d %(tsc)d dom_timer_fn
0x00080001 CPU%(cpu)d %(tsc)d VMX_VMEXIT [ domid
= 0x%(1)08x, eip = 0x%(2)08x, reason = 0x%(3)08x ]
0x00080002 CPU%(cpu)d %(tsc)d VMX_VECTOR [ domid
= 0x%(1)08x, eip = 0x%(2)08x, vector = 0x%(3)08x ]
diff -r e70ea9465b31 -r 63d05000cfa3 xen/Rules.mk
--- a/xen/Rules.mk Thu Oct 27 09:53:02 2005
+++ b/xen/Rules.mk Sun Oct 30 20:59:45 2005
@@ -6,7 +6,7 @@
debug ?= n
perfc ?= n
perfc_arrays?= n
-trace ?= n
+trace ?= y
domu_debug ?= n
crash_debug ?= n
diff -r e70ea9465b31 -r 63d05000cfa3 xen/common/trace.c
--- a/xen/common/trace.c Thu Oct 27 09:53:02 2005
+++ b/xen/common/trace.c Sun Oct 30 20:59:45 2005
@@ -5,8 +5,9 @@
*
* Copyright (C) 2004 by Intel Research Cambridge
*
- * Author: Mark Williamson, mark.a.williamson@intel.com
- * Date: January 2004
+ * Authors: Mark Williamson, mark.a.williamson@intel.com
+ * Rob Gardner, rob.gardner@hp.com
+ * Date: October 2005
*
* Copyright (C) 2005 Bin Ren
*
@@ -31,13 +32,14 @@
#include <public/dom0_ops.h>
/* opt_tbuf_size: trace buffer size (in pages) */
-static unsigned int opt_tbuf_size = 10;
+static unsigned int opt_tbuf_size = 0;
integer_param("tbuf_size", opt_tbuf_size);
/* Pointers to the meta-data objects for all system trace buffers */
struct t_buf *t_bufs[NR_CPUS];
-/* a flag recording whether initialisation has been done */
+/* a flag recording whether initialization has been done */
+/* or more properly, if the tbuf subsystem is enabled right now */
int tb_init_done = 0;
/* which CPUs tracing is enabled on */
@@ -45,25 +47,50 @@
/* which tracing events are enabled */
u32 tb_event_mask = TRC_ALL;
-/**
- * init_trace_bufs - performs initialisation of the per-cpu trace buffers.
- *
- * This function is called at start of day in order to initialise the
per-cpu
+
+/**
+ * init_trace_bufs - performs initialization of the per-cpu trace buffers.
+ *
+ * This function is called at start of day in order to initialize the
per-cpu
* trace buffers. The trace buffers are then available for debugging
use, via
* the %TRACE_xD macros exported in <xen/trace.h>.
*/
void init_trace_bufs(void)
+{
+ extern int alloc_trace_bufs(void);
+
+ if ( opt_tbuf_size == 0 )
+ {
+ printk("Xen trace buffers: disabled\n");
+ return;
+ }
+
+ if (alloc_trace_bufs() == 0) {
+ printk("Xen trace buffers: initialised\n");
+ wmb(); /* above must be visible before tb_init_done flag set */
+ tb_init_done = 1;
+ }
+}
+
+/**
+ * alloc_trace_bufs - performs initialization of the per-cpu trace buffers.
+ *
+ * This function is called at start of day in order to initialize the
per-cpu
+ * trace buffers. The trace buffers are then available for debugging
use, via
+ * the %TRACE_xD macros exported in <xen/trace.h>.
+ *
+ * This function may also be called later when enabling trace buffers
+ * via the SET_SIZE hypercall.
+ */
+int alloc_trace_bufs(void)
{
int i, order;
unsigned long nr_pages;
char *rawbuf;
struct t_buf *buf;
-
+
if ( opt_tbuf_size == 0 )
- {
- printk("Xen trace buffers: disabled\n");
- return;
- }
+ return -EINVAL;
nr_pages = num_online_cpus() * opt_tbuf_size;
order = get_order_from_pages(nr_pages);
@@ -71,7 +98,7 @@
if ( (rawbuf = alloc_xenheap_pages(order)) == NULL )
{
printk("Xen trace buffers: memory allocation failed\n");
- return;
+ return -EINVAL;
}
/* Share pages so that xentrace can map them. */
@@ -88,13 +115,50 @@
buf->rec = (struct t_rec *)(buf + 1);
buf->rec_addr = __pa(buf->rec);
}
-
- printk("Xen trace buffers: initialised\n");
-
- wmb(); /* above must be visible before tb_init_done flag set */
-
- tb_init_done = 1;
-}
+ return 0;
+}
+
+
+/**
+ * tb_set_size - handle the logic involved with dynamically
+ * allocating and deallocating tbufs
+ *
+ * This function is called when the SET_SIZE hypercall is done.
+ */
+int tb_set_size(int size)
+{
+ // There are three cases to handle:
+ // 1. Changing from 0 to non-zero ==> simple allocate
+ // 2. Changing from non-zero to 0 ==> simple deallocate
+ // 3. Changing size ==> deallocate and reallocate? Or disallow?
+ // User can just do a change to 0, then a change to the new size.
+ //
+ // Tracing must be disabled (tb_init_done==0) before calling this
+
+ if (opt_tbuf_size == 0 && size > 0) {
+ // What if size is too big? alloc_xenheap will complain.
+ opt_tbuf_size = size;
+ if (alloc_trace_bufs() != 0)
+ return -EINVAL;
+ wmb();
+ printk("Xen trace buffers: initialized\n");
+ return 0;
+ }
+ else if (opt_tbuf_size > 0 && size == 0) {
+ int order = get_order_from_pages(num_online_cpus() *
opt_tbuf_size);
+ // is there a way to undo SHARE_PFN_WITH_DOMAIN?
+ free_xenheap_pages(t_bufs[0], order);
+ opt_tbuf_size = 0;
+ printk("Xen trace buffers: uninitialized\n");
+ return 0;
+ }
+ else {
+ printk("tb_set_size from %d to %d not implemented\n",
opt_tbuf_size, size);
+ printk("change size from %d to 0, and then to %d\n",
opt_tbuf_size, size);
+ return -EINVAL;
+ }
+}
+
/**
* tb_control - DOM0 operations on trace buffers.
@@ -105,8 +169,10 @@
static spinlock_t lock = SPIN_LOCK_UNLOCKED;
int rc = 0;
- if ( !tb_init_done )
- return -EINVAL;
+ // Commenting this out since we have to allow some of these operations
+ // in order to enable dynamic control of the trace buffers.
+ // if ( !tb_init_done )
+ // return -EINVAL;
spin_lock(&lock);
@@ -123,6 +189,30 @@
break;
case DOM0_TBUF_SET_EVT_MASK:
tb_event_mask = tbc->evt_mask;
+ break;
+ case DOM0_TBUF_SET_SIZE:
+ // Change trace buffer allocation.
+ // Trace buffers must be disabled to do this.
+ if (tb_init_done) {
+ printk("attempt to change size with tbufs enabled\n");
+ rc = -EINVAL;
+ }
+ else
+ rc = tb_set_size(tbc->size);
+ break;
+ case DOM0_TBUF_ENABLE:
+ // Enable trace buffers. Size must be non-zero, ie, buffers
+ // must already be allocated.
+ if (opt_tbuf_size == 0)
+ rc = -EINVAL;
+ else
+ tb_init_done = 1;
+ break;
+ case DOM0_TBUF_DISABLE:
+ // Disable trace buffers. Just stops new records from being
written,
+ // does not deallocate any memory.
+ tb_init_done = 0;
+ printk("Xen trace buffers: disabled\n");
break;
default:
rc = -EINVAL;
diff -r e70ea9465b31 -r 63d05000cfa3 xen/include/public/dom0_ops.h
--- a/xen/include/public/dom0_ops.h Thu Oct 27 09:53:02 2005
+++ b/xen/include/public/dom0_ops.h Sun Oct 30 20:59:45 2005
@@ -193,6 +193,9 @@
#define DOM0_TBUF_GET_INFO 0
#define DOM0_TBUF_SET_CPU_MASK 1
#define DOM0_TBUF_SET_EVT_MASK 2
+#define DOM0_TBUF_SET_SIZE 3
+#define DOM0_TBUF_ENABLE 4
+#define DOM0_TBUF_DISABLE 5
uint8_t op;
/* IN/OUT variables */
unsigned long cpu_mask;
diff -r e70ea9465b31 -r 63d05000cfa3 tools/libxc/xc_tbuf.c
--- /dev/null Thu Oct 27 09:53:02 2005
+++ b/tools/libxc/xc_tbuf.c Sun Oct 30 20:59:45 2005
@@ -0,0 +1,51 @@
+/******************************************************************************
+ * xc_tbuf.c
+ *
+ * API for manipulating and accessing trace buffer parameters
+ *
+ * Copyright (c) 2005, Rob Gardner
+ */
+
+#include "xc_private.h"
+
+int xc_tbuf_enable(int xc_handle, int enable)
+{
+ dom0_op_t op;
+
+ op.cmd = DOM0_TBUFCONTROL;
+ op.interface_version = DOM0_INTERFACE_VERSION;
+ if (enable)
+ op.u.tbufcontrol.op = DOM0_TBUF_ENABLE;
+ else
+ op.u.tbufcontrol.op = DOM0_TBUF_DISABLE;
+
+ return xc_dom0_op(xc_handle, &op);
+}
+
+int xc_tbuf_set_size(int xc_handle, uint32_t size)
+{
+ dom0_op_t op;
+
+ op.cmd = DOM0_TBUFCONTROL;
+ op.interface_version = DOM0_INTERFACE_VERSION;
+ op.u.tbufcontrol.op = DOM0_TBUF_SET_SIZE;
+ op.u.tbufcontrol.size = size;
+
+ return xc_dom0_op(xc_handle, &op);
+}
+
+int xc_tbuf_get_size(int xc_handle, uint32_t *size)
+{
+ int rc;
+ dom0_op_t op;
+
+ op.cmd = DOM0_TBUFCONTROL;
+ op.interface_version = DOM0_INTERFACE_VERSION;
+ op.u.tbufcontrol.op = DOM0_TBUF_GET_INFO;
+
+ rc = xc_dom0_op(xc_handle, &op);
+ if (rc == 0)
+ *size = op.u.tbufcontrol.size;
+ return rc;
+}
+
diff -r e70ea9465b31 -r 63d05000cfa3 tools/xentrace/setsize.c
--- /dev/null Thu Oct 27 09:53:02 2005
+++ b/tools/xentrace/setsize.c Sun Oct 30 20:59:45 2005
@@ -0,0 +1,36 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <errno.h>
+#include <xenctrl.h>
+
+int main(int argc, char * argv[])
+{
+ unsigned int size;
+ int xc_handle = xc_interface_open();
+
+ if (xc_tbuf_get_size(xc_handle, &size) != 0) {
+ perror("Failure to get tbuf info from Xen. Guess size is 0.");
+ printf("This may mean that tracing is not compiled into xen.\n");
+ exit(1);
+ }
+ else
+ printf("Current tbuf size: 0x%x\n", size);
+
+ if (argc < 2)
+ exit(0);
+
+ size = atoi(argv[1]);
+
+ if (xc_tbuf_set_size(xc_handle, size) != 0) {
+ perror("set_size Hypercall failure");
+ exit(1);
+ }
+
+ if (xc_tbuf_get_size(xc_handle, &size) != 0)
+ perror("Failure to get tbuf info from Xen. Guess size is 0.");
+ else
+ printf("New tbuf size: 0x%x\n", size);
+
+ xc_interface_close(xc_handle);
+ return 0;
+}
diff -r e70ea9465b31 -r 63d05000cfa3 tools/xentrace/tbctl.c
--- /dev/null Thu Oct 27 09:53:02 2005
+++ b/tools/xentrace/tbctl.c Sun Oct 30 20:59:45 2005
@@ -0,0 +1,26 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <errno.h>
+#include <xenctrl.h>
+
+int main(int argc, char * argv[])
+{
+ int enable;
+ int xc_handle = xc_interface_open();
+
+ if (argc < 2) {
+ printf("usage: %s [0|1]\n", argv[0]);
+ exit(1);
+ }
+ enable = atoi(argv[1]);
+
+ if (xc_tbuf_enable(xc_handle, enable) != 0) {
+ perror("Enable/Disable Hypercall failure");
+ exit(1);
+ }
+ else
+ printf("Tracing now %s\n", (enable ? "enabled" :
"disabled"));
+
+ xc_interface_close(xc_handle);
+ return 0;
+}
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xensource.com
http://lists.xensource.com/xen-devel
David Hopwood
2005-Oct-30 22:53 UTC
Re: [Xen-devel] [PATCH] Changes to allow dynamic enabling/disabling of trace buffers
Rob Gardner wrote:
/**
* tb_set_size - handle the logic involved with dynamically
* allocating and deallocating tbufs
*
* This function is called when the SET_SIZE hypercall is done.
*/
int tb_set_size(int size)
{
// There are three cases to handle:
// 1. Changing from 0 to non-zero ==> simple allocate
// 2. Changing from non-zero to 0 ==> simple deallocate
// 3. Changing size ==> deallocate and reallocate? Or disallow?
// User can just do a change to 0, then a change to the new size.
They can, but the interface is slightly simpler if you allow this, and
the implementation is also slightly shorter because you don''t have to
check for the error, or comment on it:
if (opt_tbuf_size > 0) {
int order = get_order_from_pages(num_online_cpus() * opt_tbuf_size);
// is there a way to undo SHARE_PFN_WITH_DOMAIN?
free_xenheap_pages(t_bufs[0], order);
opt_tbuf_size = 0;
printk("Xen trace buffers: uninitialized\n");
}
if (size > 0) {
// What if size is too big? alloc_xenheap will complain.
opt_tbuf_size = size;
if (alloc_trace_bufs() != 0)
return -EINVAL;
wmb();
printk("Xen trace buffers: initialized\n");
}
return 0;
}
The sentence "To change the size of an existing allocation, you must first
deallocate it then reallocate it." should also be removed from the
xc_tbuf_set_size doc comment.
As a matter of style, I would also suggest moving the tb_init_done check into
tb_set_size rather than doing it in the DOM0_TBUF_SET_SIZE handler.
--
David Hopwood <david.nospam.hopwood@blueyonder.co.uk>
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xensource.com
http://lists.xensource.com/xen-devel
Rob Gardner
2005-Oct-30 22:59 UTC
Re: [Xen-devel] [PATCH] Changes to allow dynamic enabling/disabling of trace buffers
David, Thanks for your comments. I''ll make the changes you suggest. Rob David Hopwood wrote:>Rob Gardner wrote: > >/** > * tb_set_size - handle the logic involved with dynamically > * allocating and deallocating tbufs > * > * This function is called when the SET_SIZE hypercall is done. > */ >int tb_set_size(int size) >{ > // There are three cases to handle: > // 1. Changing from 0 to non-zero ==> simple allocate > // 2. Changing from non-zero to 0 ==> simple deallocate > // 3. Changing size ==> deallocate and reallocate? Or disallow? > // User can just do a change to 0, then a change to the new size. > >They can, but the interface is slightly simpler if you allow this, and >the implementation is also slightly shorter because you don''t have to >check for the error, or comment on it: > > if (opt_tbuf_size > 0) { > int order = get_order_from_pages(num_online_cpus() * opt_tbuf_size); > // is there a way to undo SHARE_PFN_WITH_DOMAIN? > free_xenheap_pages(t_bufs[0], order); > opt_tbuf_size = 0; > printk("Xen trace buffers: uninitialized\n"); > } > if (size > 0) { > // What if size is too big? alloc_xenheap will complain. > opt_tbuf_size = size; > if (alloc_trace_bufs() != 0) > return -EINVAL; > wmb(); > printk("Xen trace buffers: initialized\n"); > } > return 0; >} > >The sentence "To change the size of an existing allocation, you must first >deallocate it then reallocate it." should also be removed from the >xc_tbuf_set_size doc comment. > >As a matter of style, I would also suggest moving the tb_init_done check into >tb_set_size rather than doing it in the DOM0_TBUF_SET_SIZE handler. > > >_______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
David Hopwood
2005-Oct-30 23:02 UTC
Re: [Xen-devel] [PATCH] Changes to allow dynamic enabling/disabling of trace buffers
David Hopwood wrote:> Rob Gardner wrote: > > // 3. Changing size ==> deallocate and reallocate? Or disallow? > // User can just do a change to 0, then a change to the new size. > > They can, but the interface is slightly simpler if you allow this, and > the implementation is also slightly shorter because you don''t have to > check for the error, or comment on it:[...]> The sentence "To change the size of an existing allocation, you must first > deallocate it then reallocate it." should also be removed from the > xc_tbuf_set_size doc comment.For the implementation I gave, replace it with "If the call fails (e.g. due to lack of memory), the size may be set to zero." -- David Hopwood <david.nospam.hopwood@blueyonder.co.uk> _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Keir Fraser
2005-Oct-31 07:54 UTC
Re: [Xen-devel] [PATCH] Changes to allow dynamic enabling/disabling of trace buffers
On 30 Oct 2005, at 22:53, David Hopwood wrote:> The sentence "To change the size of an existing allocation, you must > first > deallocate it then reallocate it." should also be removed from the > xc_tbuf_set_size doc comment. > > As a matter of style, I would also suggest moving the tb_init_done > check into > tb_set_size rather than doing it in the DOM0_TBUF_SET_SIZE handler.Buffer resize was broken on SMP, so I removed it. If anyone actually cares about it then a heavier weight synchronisation will be required (perhaps in the manner of Linux''s stop_machine_run), but I''m guessing it''s not something anyone cares wildly about right now. -- Keir _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Rob Gardner
2005-Oct-31 14:42 UTC
Re: [Xen-devel] [PATCH] Changes to allow dynamic enabling/disabling of trace buffers
Keir Fraser wrote:> > Buffer resize was broken on SMP, so I removed it. If anyone actually > cares about it then a heavier weight synchronisation will be required > (perhaps in the manner of Linux''s stop_machine_run), but I''m guessing > it''s not something anyone cares wildly about right now.I think that''s correct. The main thing was to allow dynamic allocation; The resizing thing was definitely not essential. Anyway, thanks for handling that and getting it merged. Rob _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel