# HG changeset patch
# User Emmanuel Ackaouy <ack@xxxxxxxxxxxxx>
# Node ID 1940ee13f9d6ab1be2c614a0fbf7769536a056d2
# Parent 4a320d26fc24bc49ae24f31dec2bf006a9ddc7a8
Improve I/O performance when competing with CPU intensive workloads.
Allow non CPU consuming wake-to-run latency sensitive VCPUs to
preempt CPU consuming ones.
Signed-off-by: Emmanuel Ackaouy <ack@xxxxxxxxxxxxx>
---
xen/common/sched_credit.c | 30 +++++++++++++++++++++++++++++-
1 files changed, 29 insertions(+), 1 deletion(-)
diff -r 4a320d26fc24 -r 1940ee13f9d6 xen/common/sched_credit.c
--- a/xen/common/sched_credit.c Thu Oct 26 16:56:16 2006 +0100
+++ b/xen/common/sched_credit.c Fri Oct 27 15:44:27 2006 +0100
@@ -46,6 +46,7 @@
/*
* Priorities
*/
+#define CSCHED_PRI_TS_BOOST 0 /* time-share waking up */
#define CSCHED_PRI_TS_UNDER -1 /* time-share w/ credits */
#define CSCHED_PRI_TS_OVER -2 /* time-share w/o credits */
#define CSCHED_PRI_IDLE -64 /* idle */
@@ -410,6 +411,14 @@ csched_vcpu_acct(struct csched_vcpu *svc
spin_unlock_irqrestore(&csched_priv.lock, flags);
}
+
+ /*
+ * If this VCPU's priority was boosted when it last awoke, reset it.
+ * If the VCPU is found here, then it's consuming a non-negligeable
+ * amount of CPU resources and should no longer be boosted.
+ */
+ if ( svc->pri == CSCHED_PRI_TS_BOOST )
+ svc->pri = CSCHED_PRI_TS_UNDER;
}
static inline void
@@ -566,6 +575,25 @@ csched_vcpu_wake(struct vcpu *vc)
else
CSCHED_STAT_CRANK(vcpu_wake_not_runnable);
+ /*
+ * We temporarly boost the priority of awaking VCPUs!
+ *
+ * If this VCPU consumes a non negligeable amount of CPU, it
+ * will eventually find itself in the credit accounting code
+ * path where its priority will be reset to normal.
+ *
+ * If on the other hand the VCPU consumes little CPU and is
+ * blocking and awoken a lot (doing I/O for example), its
+ * priority will remain boosted, optimizing it's wake-to-run
+ * latencies.
+ *
+ * This allows wake-to-run latency sensitive VCPUs to preempt
+ * more CPU resource intensive VCPUs without impacting overall
+ * system fairness.
+ */
+ if ( svc->pri == CSCHED_PRI_TS_UNDER )
+ svc->pri = CSCHED_PRI_TS_BOOST;
+
/* Put the VCPU on the runq and tickle CPUs */
__runq_insert(cpu, svc);
__runq_tickle(cpu, svc);
@@ -659,7 +687,7 @@ csched_runq_sort(unsigned int cpu)
next = elem->next;
svc_elem = __runq_elem(elem);
- if ( svc_elem->pri == CSCHED_PRI_TS_UNDER )
+ if ( svc_elem->pri >= CSCHED_PRI_TS_UNDER )
{
/* does elem need to move up the runq? */
if ( elem->prev != last_under )
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