linux-kernel - Re: [PATCH] [RT] avoid preemption in memory controller code

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Message-Id: <1228756056.7862.8.camel@thinkpad>
Date:	Mon, 08 Dec 2008 18:07:36 +0100
From:	Tim Blechmann <tim@...ngt.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-rt-users <linux-rt-users@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] [RT] avoid preemption in memory controller code

> > the lru_lock of struct mem_group_per_zone is used to avoid preemption
> > during the __mem_cgroup_stat_add_safe function.
> > therefore, a raw_spinlock_t should be used.
> 
> What is the reason that this must avoid preemption? 

it guards a call to smp_processor_id() in __mem_cgroup_stat_add_safe().
see http://article.gmane.org/gmane.linux.rt.user/3690

> Is there another
> way to solve this? I rather not just add a raw spinlock if we can
> help it.

not sure, maybe one can disable preemption for that specific function?

tim

--
tim@...ngt.org
http://tim.klingt.org

Art is either a complaint or do something else
  John Cage quoting Jasper Johns

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