linux-kernel - Re: Steal time accounting in KVM. Benchmark.

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Date:	Tue, 20 Oct 2015 13:05:18 -0700
From:	Alexey Makhalov <makhaloff@...il.com>
To:	Wanpeng Li <kernellwp@...il.com>
Cc:	kvm <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	wanpeng.li@...mail.com, Peter Zijlstra <peterz@...radead.org>,
	Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: Steal time accounting in KVM. Benchmark.

'echo NO_NONTASK_CAPACITY > /sys/kernel/debug/sched_features'  in both guests.
Results:
VM1: STA is disabled -- no changes, still little bit bellow expected 90%
VM2: STA is enabled -- result is changed, but still bad. Hard to say
better or worse. It prefers to stuck at quarters (100% 75% 50% 25%)
Output is attached.

Thanks,
Alexey

On Tue, Oct 20, 2015 at 5:39 AM, Wanpeng Li <kernellwp@...il.com> wrote:
> Cc Peterz,
> 2015-10-20 5:58 GMT+08:00 Alexey Makhalov <makhaloff@...il.com>:
>>
>> Hi,
>>
>> I did benchmarking of scheduler fairness with enabled steal time
>> accounting(STA) in KVM.
>> And results are really interesting.
>>
>> Looks like STA provides worse scheduler fairness against disabled STA
>> (no-steal-acc cmdline param)
>>
>> I created benchmark, main idea is: 2 cgroups with cpu.shares
>> proportion like 1/9, run identical work in both groups, and expecting
>> to get the same proportion of work done – 1/9. Condition – CPU
>> overcommit.
>>
>> On bare metal it is fair +- some percentages of fluctation.
>> On KVM with no STA   it’s less fair. With STA enabled results are
>> ugly! One again – in CPU overcommit situation.
>>
>>
>> Host: ubuntu 14.04, Intel i5 – 2x2 CPUs
>> 2 VMs (4 vCPU each) are working in parallel.   2:1 cpu overcommit.
>>
>> Each VM has running benchmark:
>> cgroups cpu.shares proportion is 128/1152 (10%/90%), work – spinning
>> in cycle, number of cycles are being counted.
>
>
> Could you try if 'echo NO_NONTASK_CAPACITY >
> /sys/kernel/debug/sched_features' in guests works?
>
> Regards,
> Wanpeng Li

View attachment "no_nontask_capacity.txt" of type "text/plain" (4250 bytes)