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

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Message-ID: <CA+icZUWJSZT+TUMynsFKd-_3x-TMB=NeK+6f2cWsi6-g82rWKA@mail.gmail.com>
Date:	Thu, 31 Jan 2013 08:24:22 +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 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?
What about the other parts? Coming later?

>>
>> Does the latter need no more EXPORT_SYMBOL_GPL for vtime_guest_enter()
>> and vtime_guest_exit() when CONFIG_KVM=m (see [1])?
>
> It doesn't need export symbol on vtime_guest_() APIs, only on
> guest_enter and guest_exit.
>

I verified this by building by myself.

- Sedat -

> Thanks.
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