linux-kernel - Re: [PATCH 8/8] cputime: Safely read cputime of full dynticks CPUs

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Date:	Thu, 31 Jan 2013 11:30:59 +0100
From:	Sedat Dilek <sedat.dilek@...il.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Li Zhong <zhong@...ux.vnet.ibm.com>,
	Namhyung Kim <namhyung.kim@....com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 8/8] cputime: Safely read cputime of full dynticks CPUs

On Thu, Jan 31, 2013 at 11:12 AM, Frederic Weisbecker
<fweisbec@...il.com> wrote:
> 2013/1/31 Sedat Dilek <sedat.dilek@...il.com>:
>> On Thu, Jan 31, 2013 at 1:38 AM, Frederic Weisbecker <fweisbec@...il.com> wrote:
>>> 2013/1/28 Sedat Dilek <sedat.dilek@...il.com>:
>>>> On Mon, Jan 28, 2013 at 8:04 PM, Frederic Weisbecker <fweisbec@...il.com> wrote:
>>>>> While remotely reading the cputime of a task running in a
>>>>> full dynticks CPU, the values stored in utime/stime fields
>>>>> of struct task_struct may be stale. Its values may be those
>>>>> of the last kernel <-> user transition time snapshot and
>>>>> we need to add the tickless time spent since this snapshot.
>>>>>
>>>>> To fix this, flush the cputime of the dynticks CPUs on
>>>>> kernel <-> user transition and record the time / context
>>>>> where we did this. Then on top of this snapshot and the current
>>>>> time, perform the fixup on the reader side from task_times()
>>>>> accessors.
>>>>>
>>>>> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
>>>>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>>>>> Cc: Ingo Molnar <mingo@...nel.org>
>>>>> Cc: Li Zhong <zhong@...ux.vnet.ibm.com>
>>>>> Cc: Namhyung Kim <namhyung.kim@....com>
>>>>> Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
>>>>> Cc: Paul Gortmaker <paul.gortmaker@...driver.com>
>>>>> Cc: Peter Zijlstra <peterz@...radead.org>
>>>>> Cc: Steven Rostedt <rostedt@...dmis.org>
>>>>> Cc: Thomas Gleixner <tglx@...utronix.de>
>>>>> [fixed kvm module related build errors]
>>>>> Signed-off-by: Sedat Dilek <sedat.dilek@...il.com>
>>>>>
>>>>
>>>> Can you explain a bit what is the difference between "3.8-rc4-nohz3"
>>>> and "full-dynticks-cputime-for-mingo" patchsets?
>>>
>>> 3.8-rc4-nohz3 is the latest experimental tree that implements full
>>> dynticks. It includes an earlier version of full dynticks cputime and
>>> many other things to make the full dynticks possible: nohz printk,
>>> many tweaks on the scheduler and timers...etc
>>>
>>
>> So, dynticks-cputime will go into 3.9?
>
> I can't say "will" but I hope.
>
>> What about the other parts? Coming later?
>
> May be the printk part will go into 3.9. Linus ignored my pull request
> so may be we'll get more chances if it goes through Ingo.
>

I still dunno all parts of dynticks and their correlation.
AFAICS they seem to be independent, can't say if it is "complete" with
dynticks-cputime-only.

Was that dynticks stuff ever advertised for Linux-Next inclusion?
Or wnt through any "mingo-next" tree?
AFAICS, better chances these ways!

- Sedat -

> And the rest will come later.
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