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Date: Wed, 18 Jan 2012 10:09:25 +0800
From: David Xu <listlog2011@gmail.com>
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To: John Baldwin <jhb@freebsd.org>
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Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org,
	src-committers@freebsd.org, David Xu <davidxu@freebsd.org>
Subject: Re: svn commit: r230201 - head/lib/libc/gen
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On 2012/1/17 22:57, John Baldwin wrote:
> On Monday, January 16, 2012 1:15:14 am David Xu wrote:
>> Author: davidxu
>> Date: Mon Jan 16 06:15:14 2012
>> New Revision: 230201
>> URL: http://svn.freebsd.org/changeset/base/230201
>>
>> Log:
>>    Insert read memory barriers.
> I think using atomic_load_acq() on sem->nwaiters would be clearer as it would
> indicate which variable you need to ensure is read after other operations.  In
> general I think raw rmb/wmb usage should be avoided when possible as it is
> does not describe the programmer's intent as well.
>
Yes, I had considered that I may use atomic_load_acq(), but at that time,
I thought it emits a bus locking, right ? so I just picked up rmb() which
only affects current cpu. maybe atomic_load_acq() does same thing with 
rmb() ?
it is still unclear to me.

Regards,
David Xu