Date: Fri, 20 Jan 2012 08:36:33 +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, davidxu@freebsd.org Subject: Re: svn commit: r230201 - head/lib/libc/gen Message-ID: <4F18B711.9000406@gmail.com> In-Reply-To: <201201191023.28426.jhb@freebsd.org> References: <201201160615.q0G6FE9r019542@svn.freebsd.org> <4F178CDC.3030807@gmail.com> <4F17B0DE.3060008@gmail.com> <201201191023.28426.jhb@freebsd.org>
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On 2012/1/19 23:23, John Baldwin wrote: > On Thursday, January 19, 2012 12:57:50 am David Xu wrote: >> rdtsc() may not work on SMP, so I have updated it to use clock_gettime >> to get total time. >> http://people.freebsd.org/~davidxu/bench/semaphore2/ >> <http://people.freebsd.org/%7Edavidxu/bench/semaphore2/>; >> >> Still, lfence is a lot faster than atomic lock. > http://www.freebsd.org/~jhb/patches/amd64_fence.patch > > This the patch I've had for quite a while. Can you retest with this? You'll > probably have to install the updated header in /usr/include as well. > The lines in atomic_load_acq() seem not what I want: + v = *p; \ + __asm __volatile("lfence" ::: "memory"); \ I think they should be swapped ? + __asm __volatile("lfence" ::: "memory"); \ + v = *p; \ What I need in the semaphore code is read can not pass write in such a special case.
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