Re: [RFC] eventpoll: Move a kmem_cache_alloc and kmem_cache_free

[Nathan Zimmer]

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 https://lkml.org/lkml/2011/2/25/297.
> >
> > 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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