Re: [PATCH 1/2] brw_mutex: big read-write mutex

From: Oleg Nesterov
Date: Fri Oct 19 2012 - 13:56:43 EST

On 10/19, Peter Zijlstra wrote:
> But using preempt_{disable,enable} and using synchronize_sched() would
> be better (for PREEMPT_RCU) although it wouldn't fix anything
> fundamental.

BTW, I agree. I didn't even notice percpu-rwsem.h uses _rcu, not _sched.

> Fine goal, although somewhat arch specific. Also note that there's a
> relation between atomics and memory barriers, one isn't necessarily
> worse than the other, they all require synchronization of sorts.

As Paul pointed out, the fast path can avoid mb(). It is only needed
when "up_read" detects the writer.


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