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Subject: Re: [PATCH 4/4] cpuset,mm: use rwlock to protect task->mempolicy
 and mems_allowed
From: Peter Zijlstra <peterz@infradead.org>
To: Nick Piggin <npiggin@suse.de>
Cc: Miao Xie <miaox@cn.fujitsu.com>, David Rientjes <rientjes@google.com>,
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Date: Thu, 04 Mar 2010 15:58:24 +0100
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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.