Date: Wed, 18 Jan 2012 10:09:25 +0800 From: David Xu <listlog2011@gmail.com> To: John Baldwin <jhb@freebsd.org> 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 Message-ID: <4F1629D5.4020605@gmail.com> In-Reply-To: <201201170957.47718.jhb@freebsd.org> References: <201201160615.q0G6FE9r019542@svn.freebsd.org> <201201170957.47718.jhb@freebsd.org>
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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
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