linux-kernel - Re: [PATCH v5 3/3] sched/cputime: Add steal time support to full dynticks CPU time accounting

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Date:	Wed, 8 Jun 2016 16:12:25 +0800
From:	Wanpeng Li <kernellwp@...il.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Rik van Riel <riel@...hat.com>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	kvm <kvm@...r.kernel.org>, Wanpeng Li <wanpeng.li@...mail.com>,
	"Peter Zijlstra (Intel)" <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [PATCH v5 3/3] sched/cputime: Add steal time support to full
 dynticks CPU time accounting

2016-06-08 16:04 GMT+08:00 Wanpeng Li <kernellwp@...il.com>:
> 2016-06-08 15:52 GMT+08:00 Ingo Molnar <mingo@...nel.org>:
>>
>> * Wanpeng Li <kernellwp@...il.com> wrote:
>>
>>> 2016-06-08 15:22 GMT+08:00 Ingo Molnar <mingo@...nel.org>:
>>> >
>>> > * Wanpeng Li <kernellwp@...il.com> wrote:
>>> >
>>> >> From: Wanpeng Li <wanpeng.li@...mail.com>
>>> >>
>>> >> This patch adds guest steal-time support to full dynticks CPU
>>> >> time accounting. After the following commit:
>>> >>
>>> >> ff9a9b4c4334 ("sched, time: Switch VIRT_CPU_ACCOUNTING_GEN to jiffy granularity")
>>> >>
>>> >> ... time sampling became jiffy based, even if it's still listened
>>> >> to ring boundaries, so steal_account_process_tick() is reused
>>> >> to account how many 'ticks' are stolen-time, after the last accumulation.
>>> >
>>> > So the 'ring boundary' part still doesn't parse (neither grammatically nor
>>> > logically) - please rephrase it because I have no idea what you want to say here.
>>>
>>> It is original from this slides.
>>> http://ertl.jp/~shinpei/conf/ospert13/slides/FredericWeisbecker.pdf,
>>> slide 28.
>>
>> Yes, I now understand that this is meant as 'context tracking is active', but I
>> don't understand the way you use it in this changelog's context.
>>
>> Btw., the grammatically correct way to add that phrase would have been:
>>
>>  ... time sampling became jiffy based, even if it's still listening to ring
>>  boundaries, so steal_account_process_tick() is reused to account how many
>>  'ticks' are stolen-time, after the last accumulation.
>
> Thanks, Ingo!
>
>>
>> But I still don't understand it, nor did Paolo understand it.
>>
>> Nor is there any 0/3 boilerplace description that gives some context about what
>> these changes are about. Exactly what do you mean by 'add steal-time support' - we
>> clearly had that before. So is your patch lifting some limitation? Or was
>> steal-time accounting totally inactive with certain dynticks configurations? The
>> changelog does not tell us anything about that...
>
> Now I understand why you said "write-only code". vtime(depends on
> context tracking) which is just used in full dynamic doesn't account

s/dynamic/dynticks

> steal time, however, periodic/nohz idle which not use vtime have codes
> account steal time in cputime.c, this patch add the steal time
> acccount support in vtime which will be used in full dynamic guest.

s/dynamic/dynticks

>
> Regards,
> Wanpeng Li



-- 
Regards,
Wanpeng Li