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

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Message-ID: <CALd+sgfA1MVObNwXegqSc1cCyo1FeKqpP6SLHc6WdU44tdy24w@mail.gmail.com>
Date:	Fri, 23 Oct 2015 19:03:38 -0700
From:	Alexey Makhalov <makhaloff@...il.com>
To:	Wanpeng Li <wanpeng.li@...mail.com>
Cc:	kvm <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: Steal time accounting in KVM. Benchmark.

 What I figured out.
It happens in intersection of 3 features:
*irq time accounting
*stolen time accounting
*linux guest with tickless idle only (not fully tickless)

Looks like timer interrupts storm is happening during this benchmark
(with 2:1 cpu overcommit). irq time accounting gets crazy. Even 'top'
shows weird statistic: 50% hi, 50% st, ~0% user, spinning processes
use ~0% cpu - that is not correct.

Thanks.


On Tue, Oct 20, 2015 at 5:24 PM, Alexey Makhalov <makhaloff@...il.com> wrote:
> Yes, VM1 results are as before.
>
> Alexey
>
> On Tue, Oct 20, 2015 at 4:04 PM, Wanpeng Li <wanpeng.li@...mail.com> wrote:
>> On 10/21/15 4:05 AM, Alexey Makhalov wrote:
>>>
>>> '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.
>>
>>
>> If the output in attachment is for VM2 only?
>>
>> Regards,
>> Wanpeng Li
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