linux-kernel - Re: [PATCH 2/3] context_tracking: Inherit TIF_NOHZ through forks instead of context switches

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Message-ID: <551D852C.90000@redhat.com>
Date:	Thu, 02 Apr 2015 14:06:36 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Dave Jones <davej@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Oleg Nesterov <oleg@...hat.com>,
	"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 2/3] context_tracking: Inherit TIF_NOHZ through forks
 instead of context switches

On 04/02/2015 01:39 PM, Frederic Weisbecker wrote:
> TIF_NOHZ is used by context_tracking to force syscall slow-path on every
> task in order to track userspace roundtrips. As such, it must be set on
> all running tasks.
> 
> It's currently explicitly inherited through context switches. There is
> no need to do it on this fast-path though. The flag could be simply
> set once for all on all tasks, whether they are running or not.
> 
> Lets do this by setting the flag to init task on early boot and let it
> propagate through fork inheritance.
> 
> Suggested-by: Oleg Nesterov <oleg@...hat.com>
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Rik van Riel <riel@...hat.com>
> Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Dave Jones <davej@...hat.com>
> Cc: Oleg Nesterov <oleg@...hat.com>

Reviewed-by: Rik van Riel <riel@...hat.coM>

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