From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nathan Zimmer Subject: Re: [RFC] eventpoll: Move a kmem_cache_alloc and kmem_cache_free Date: Thu, 19 Sep 2013 11:37:59 -0500 Message-ID: <523B2867.7000209@sgi.com> References: <1379087642-131349-1-git-send-email-nzimmer@sgi.com> <5239FA69.8030202@akamai.com> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit Cc: , , Al Viro To: Jason Baron Return-path: In-Reply-To: <5239FA69.8030202@akamai.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org 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.