linux-kernel - Re: [PATCH RT 4/5] allow preemption in mem_cgroup_move_account_page

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Message-ID: <20140214153034.GA4015@opentech.at>
Date:	Fri, 14 Feb 2014 16:30:34 +0100
From:	Nicholas Mc Guire <der.herr@...r.at>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:	linux-rt-users@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Carsten Emde <C.Emde@...dl.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andreas Platschek <platschek@....tuwien.ac.at>
Subject: Re: [PATCH RT 4/5] allow preemption in
	mem_cgroup_move_account_page_stat

On Fri, 14 Feb 2014, Sebastian Andrzej Siewior wrote:

> * Sebastian Andrzej Siewior | 2014-02-14 14:17:05 [+0100]:
> 
> >Now, that I look at it again. Isn't it more efficient to keep preemption
> >disabled for this very short time instead instead of invoking
> >migrate_disable() which includes preempt_disable()/enable() and a few
> >more opcodes???
> >Therefore, I drop it again.
> 
> I think doing the same for the 1/5 of this series since it also disables
> migration for a handfull of asm opcodes.
>
yup - nice run in the wrong direction :)
those short pushdowns make no sense - should have looked at that first...
the execution length/complexity (notably worst case on migrate_enable()) is
actually very high compared to a preempt_enable.

thx!
hofrat
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