On 08/10/2013 09:17 PM, Mike Galbraith wrote:
>>
>> Do you have any quantification of "munches throughput?" It seems odd
>> that it would be worse than polling for preempt all over the kernel, but
>> perhaps the additional locking is what costs.
>
> I hadn't compared in ages, so made some fresh samples.
>
> Q6600 3.11-rc4
>
> vmark
> voluntary 169808 155826 154741 1.000
> preempt 149354 124016 128436 .836
>
> That should be ~worst case, it hates preemption.
>
> tbench 8
> voluntary 1027.96 1028.76 1044.60 1.000
> preempt 929.06 935.01 928.64 .900
>
> hackbench -l 10000
> voluntary 23.146 23.124 23.230 1.000
> preempt 25.065 24.633 24.789 1.071
>
> kbuild vmlinux
> voluntary 3m44.842s 3m42.975s 3m42.954s 1.000
> preempt 3m46.141s 3m45.835s 3m45.953s 1.010
>
> Compute load comparisons are boring 'course.
>
I presume voluntary is indistinguishable from no preemption at all?
Either way, that is definitely a reproducible test case, so if someone
is willing to take on optimizing preemption they can use vmark as the
litmus test. It would be really awesome if we genuinely could get the
cost of preemption down to where it just doesn't matter.
-hpa
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