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SubjectRe: [RFC] eventpoll: Move a kmem_cache_alloc and kmem_cache_free
On 09/18/2013 02:09 PM, Jason Baron wrote:
> On 09/13/2013 11:54 AM, Nathan Zimmer wrote:
>> We noticed some scaling issue in the SPECjbb benchmark. Running perf
>> we found that the it was spending lots of time in SYS_epoll_ctl.
>> In particular it is holding the epmutex.
>> This patch helps by moving out the kmem_cache_alloc and kmem_cache_free out
>> from under the lock. It improves throughput by around 15% on 16 sockets.
>> While this patch should be fine as it is there are probably is more things
>> that can be done out side the lock, like wakeup_source_unregister, but I am
>> not familar with the area and I don't know of many tests. I did find the
>> one posted by Jason Baron at
>> Any thoughts?
> Hi,
> Intersting - I think its also possible to completely drop taking the
> 'epmutex' for EPOLL_CTL_DEL by using rcu, and restricting it on add
> to more 'complex' topologies. That is when we have an epoll descriptor
> that doesn't nest with other epoll descriptors, we don't need the
> global 'epmutex' either. Any chance you can re-run with this? Its a bit
> hacky, but we can clean it up if it makes sense.
> Thanks,
> -Jason
That is working GREAT. It is scaling to 16 jobs quite well.
I will have to grab a larger machine( to see what the new scaling curve
will be.

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