From 59f9d8ef4489a9f13397c5115904e230720f23be Mon Sep 17 00:00:00 2001 From: Emmanuel Ackaouy Date: Fri, 27 Oct 2006 15:44:27 +0100 Subject: [PATCH] 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 --- xen/common/sched_credit.c | 30 +++++++++++++++++++++++++++++- 1 file changed, 29 insertions(+), 1 deletion(-) diff --git a/xen/common/sched_credit.c b/xen/common/sched_credit.c index 1dd54bbf52..32b09685ab 100644 --- a/xen/common/sched_credit.c +++ b/xen/common/sched_credit.c @@ -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, int credit_dec) 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 ) -- 2.30.2