Messages in this thread | | | Date | Thu, 14 Aug 2008 10:05:54 -0700 | From | Jeremy Fitzhardinge <> | Subject | Re: [RFC PATCH] x86 alternatives : fix LOCK_PREFIX race with preemptible kernel and CPU hotplug |
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Mathieu Desnoyers wrote: > * H. Peter Anvin (hpa@zytor.com) wrote: > >> Mathieu Desnoyers wrote: >> >>> I can't argue about the benefit of using VM CPU pinning to manage >>> resources because I don't use it myself, but I ran some tests out of >>> curiosity to find if uncontended locks were that cheap, and it turns out >>> they aren't. Here are the results : >>> Xeon 2.0GHz >>> Summary >>> make -j1 kernel/ 33.94 +/- 0.07 34.91 +/- 0.27 2.8 % >>> hackbench 50 2.99 +/- 0.01 3.74 +/- 0.01 25.1 % >>> 1 CPU, replace smp lock prefixes with DS segment selector prefixes >>> 1 CPU, noreplace-smp >>> >> For reference, could you also compare replace smp lock with NOPs? >> >> -hpa >> > > Sure, here are the updated tables. Basically, they show no significant > difference between the NOP and the DS segment selector prefix > approaches. >
BTW, are you changing the initial prefix to DS too? Ie, are you doing a nop->lock->ds transition, or ds->lock->ds?
J
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