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

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Message-ID: <CA+icZUWdGCytVsNKK+gA7Sh-RKT-GPCHoRtPNfDw4_Hfh+ynyA@mail.gmail.com>
Date:	Mon, 28 Jan 2013 22:51:22 +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 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?

Does the latter need no more EXPORT_SYMBOL_GPL for vtime_guest_enter()
and vtime_guest_exit() when CONFIG_KVM=m (see [1])?

- Sedat -

[1] https://lkml.org/lkml/2013/1/23/473
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