Messages in this thread | | | Date | Sun, 27 Jan 2013 22:28:37 +0530 | From | Raghavendra K T <> | Subject | Re: [PATCH V3 RESEND RFC 1/2] sched: Bail out of yield_to when source and target runqueue has one task |
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On 01/26/2013 12:19 AM, Ingo Molnar wrote: > > * Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com> wrote: > >> On 01/25/2013 04:17 PM, Ingo Molnar wrote: >>> >>> * Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com> wrote: >>> >>>> * Ingo Molnar <mingo@kernel.org> [2013-01-24 11:32:13]: >>>> >>>>> >>>>> * Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com> wrote: >>>>> >>>>>> From: Peter Zijlstra <peterz@infradead.org> >>>>>> >>>>>> In case of undercomitted scenarios, especially in large guests >>>>>> yield_to overhead is significantly high. when run queue length of >>>>>> source and target is one, take an opportunity to bail out and return >>>>>> -ESRCH. This return condition can be further exploited to quickly come >>>>>> out of PLE handler. >>>>>> >>>>>> (History: Raghavendra initially worked on break out of kvm ple handler upon >>>>>> seeing source runqueue length = 1, but it had to export rq length). >>>>>> Peter came up with the elegant idea of return -ESRCH in scheduler core. >>>>>> >>>>>> Signed-off-by: Peter Zijlstra <peterz@infradead.org> >>>>>> Raghavendra, Checking the rq length of target vcpu condition added.(thanks Avi) >>>>>> Reviewed-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com> >>>>>> Signed-off-by: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com> >>>>>> Acked-by: Andrew Jones <drjones@redhat.com> >>>>>> Tested-by: Chegu Vinod <chegu_vinod@hp.com> >>>>>> --- >>>>>> >>>>>> kernel/sched/core.c | 25 +++++++++++++++++++------ >>>>>> 1 file changed, 19 insertions(+), 6 deletions(-) >>>>>> >>>>>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c >>>>>> index 2d8927f..fc219a5 100644 >>>>>> --- a/kernel/sched/core.c >>>>>> +++ b/kernel/sched/core.c >>>>>> @@ -4289,7 +4289,10 @@ EXPORT_SYMBOL(yield); >>>>>> * It's the caller's job to ensure that the target task struct >>>>>> * can't go away on us before we can do any checks. >>>>>> * >>>>>> - * Returns true if we indeed boosted the target task. >>>>>> + * Returns: >>>>>> + * true (>0) if we indeed boosted the target task. >>>>>> + * false (0) if we failed to boost the target. >>>>>> + * -ESRCH if there's no task to yield to. >>>>>> */ >>>>>> bool __sched yield_to(struct task_struct *p, bool preempt) >>>>>> { >>>>>> @@ -4303,6 +4306,15 @@ bool __sched yield_to(struct task_struct *p, bool preempt) >>>>>> >>>>>> again: >>>>>> p_rq = task_rq(p); >>>>>> + /* >>>>>> + * If we're the only runnable task on the rq and target rq also >>>>>> + * has only one task, there's absolutely no point in yielding. >>>>>> + */ >>>>>> + if (rq->nr_running == 1 && p_rq->nr_running == 1) { >>>>>> + yielded = -ESRCH; >>>>>> + goto out_irq; >>>>>> + } >>>>> >>>>> Looks good to me in principle. >>>>> >>>>> Would be nice to get more consistent benchmark numbers. Once >>>>> those are unambiguously showing that this is a win: >>>>> >>>>> Acked-by: Ingo Molnar <mingo@kernel.org> >>>>> >>>> >>>> I ran the test with kernbench and sysbench again on 32 core mx3850 >>>> machine with 32 vcpu guests. Results shows definite improvements. >>>> >>>> ebizzy and dbench show similar improvement for 1x overcommit >>>> (note that stdev for 1x in dbench is lesser improvemet is now seen at >>>> only 20%) >>>> >>>> [ all the experiments are taken out of 8 run averages ]. >>>> >>>> The patches benefit large guest undercommit scenarios, so I believe >>>> with large guest performance improvemnt is even significant. [ Chegu >>>> Vinod results show performance near to no ple cases ]. Unfortunately I >>>> do not have a machine to test larger guest (>32). >>>> >>>> Ingo, Please let me know if this is okay to you. >>>> >>>> base kernel = 3.8.0-rc4 >>>> >>>> +-----------+-----------+-----------+------------+-----------+ >>>> kernbench (time in sec lower is better) >>>> +-----------+-----------+-----------+------------+-----------+ >>>> base stdev patched stdev %improve >>>> +-----------+-----------+-----------+------------+-----------+ >>>> 1x 46.6028 1.8672 42.4494 1.1390 8.91234 >>>> 2x 99.9074 9.1859 90.4050 2.6131 9.51121 >>>> +-----------+-----------+-----------+------------+-----------+ >>>> +-----------+-----------+-----------+------------+-----------+ >>>> sysbench (time in sec lower is better) >>>> +-----------+-----------+-----------+------------+-----------+ >>>> base stdev patched stdev %improve >>>> +-----------+-----------+-----------+------------+-----------+ >>>> 1x 18.7402 0.3764 17.7431 0.3589 5.32065 >>>> 2x 13.2238 0.1935 13.0096 0.3152 1.61981 >>>> +-----------+-----------+-----------+------------+-----------+ >>>> >>>> +-----------+-----------+-----------+------------+-----------+ >>>> ebizzy (records/sec higher is better) >>>> +-----------+-----------+-----------+------------+-----------+ >>>> base stdev patched stdev %improve >>>> +-----------+-----------+-----------+------------+-----------+ >>>> 1x 2421.9000 19.1801 5883.1000 112.7243 142.91259 >>>> +-----------+-----------+-----------+------------+-----------+ >>>> >>>> +-----------+-----------+-----------+------------+-----------+ >>>> dbench (throughput MB/sec higher is better) >>>> +-----------+-----------+-----------+------------+-----------+ >>>> base stdev patched stdev %improve >>>> +-----------+-----------+-----------+------------+-----------+ >>>> 1x 11675.9900 857.4154 14103.5000 215.8425 20.79061 >>>> +-----------+-----------+-----------+------------+-----------+ >>> >>> The numbers look pretty convincing, thanks. The workloads were >>> CPU bound most of the time, right? >> >> Yes. CPU bound most of the time. I also used tmpfs to reduce >> io overhead (for dbbench). > > Ok, cool. > > Which tree will this be upstreamed through - the KVM tree? I'd > suggest the KVM tree because KVM will be the one exposed to the > effects of this change.
Thanks Ingo.
Marcelo, Could you please take this into kvm tree.. ?
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