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SubjectRe: [RFC PATCH] x86 alternatives : fix LOCK_PREFIX race with preemptible kernel and CPU hotplug
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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