linux-kernel - Re: [PATCH 4/4] cpuset,mm: use rwlock to protect task->mempolicy and mems

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Message-ID: <1267714704.25158.199.camel@laptop>
Date:	Thu, 04 Mar 2010 15:58:24 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Nick Piggin <npiggin@...e.de>
Cc:	Miao Xie <miaox@...fujitsu.com>,
	David Rientjes <rientjes@...gle.com>,
	Lee Schermerhorn <lee.schermerhorn@...com>,
	Paul Menage <menage@...gle.com>,
	Linux-Kernel <linux-kernel@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>, tglx <tglx@...utronix.de>
Subject: Re: [PATCH 4/4] cpuset,mm: use rwlock to protect task->mempolicy
 and mems_allowed

On Thu, 2010-03-04 at 14:30 +1100, Nick Piggin wrote:
> 
> Thanks for working on this. However, rwlocks are pretty nasty to use
> when you have short critical sections and hot read-side (they're twice
> as heavy as even spinlocks in that case). 

Should we add a checkpatch.pl warning for them? 

There really rarely is a good case for using rwlock_t, for as you say
they're a pain and often more expensive than a spinlock_t, and if
possible RCU has the best performance.

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