Jan Beulich
2013-Feb-26 15:44 UTC
[PATCH v2] credit1: track residual from divisions done during accounting
This should help with under-accounting of vCPU-s running for extremly
short periods of time, but becoming runnable again at a high frequency.
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: George Dunlap <george.dunlap@eu.citrix.com>
---
v2: Comment ASSERT() and drop credit2 portion upon George''s request.
--- a/xen/common/sched_credit.c
+++ b/xen/common/sched_credit.c
@@ -19,6 +19,7 @@
#include <xen/sched-if.h>
#include <xen/softirq.h>
#include <asm/atomic.h>
+#include <asm/div64.h>
#include <xen/errno.h>
#include <xen/keyhandler.h>
#include <xen/trace.h>
@@ -136,6 +137,7 @@ struct csched_vcpu {
struct csched_dom *sdom;
struct vcpu *vcpu;
atomic_t credit;
+ unsigned int residual;
s_time_t start_time; /* When we were scheduled (used for credit) */
uint16_t flags;
int16_t pri;
@@ -242,6 +244,7 @@ __runq_remove(struct csched_vcpu *svc)
static void burn_credits(struct csched_vcpu *svc, s_time_t now)
{
s_time_t delta;
+ uint64_t val;
unsigned int credits;
/* Assert svc is current */
@@ -250,7 +253,10 @@ static void burn_credits(struct csched_v
if ( (delta = now - svc->start_time) <= 0 )
return;
- credits = (delta*CSCHED_CREDITS_PER_MSEC + MILLISECS(1)/2) / MILLISECS(1);
+ val = delta * CSCHED_CREDITS_PER_MSEC + svc->residual;
+ svc->residual = do_div(val, MILLISECS(1));
+ credits = val;
+ ASSERT(credits == val); /* make sure we haven''t truncated val */
atomic_sub(credits, &svc->credit);
svc->start_time += (credits * MILLISECS(1)) / CSCHED_CREDITS_PER_MSEC;
}
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