From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: Re: [RFC PATCH 0/4] cgroup aware workqueues Date: Thu, 31 Mar 2016 13:14:35 -0400 Message-ID: <20160331171435.GD24661@htj.duckdns.org> References: <1458339291-4093-1-git-send-email-bsd@redhat.com> <201603210758.u2L7wiY9003907@d06av07.portsmouth.uk.ibm.com> <20160330170419.GG7822@mtj.duckdns.org> <201603310617.u2V6HIkt008006@d06av12.portsmouth.uk.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Bandan Das , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, mst@redhat.com, jiangshanlai@gmail.com To: Michael Rapoport Return-path: Content-Disposition: inline In-Reply-To: <201603310617.u2V6HIkt008006@d06av12.portsmouth.uk.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org Hello, Michael. On Thu, Mar 31, 2016 at 08:17:13AM +0200, Michael Rapoport wrote: > > There really shouldn't be any difference when using unbound > > workqueues. workqueue becomes a convenience thing which manages > > worker pools and there shouldn't be any difference between workqueue > > workers and kthreads in terms of behavior. > > I agree that there really shouldn't be any performance difference, but the > tests I've run show otherwise. I have no idea why and I hadn't time yet to > investigate it. I'd be happy to help digging into what's going on. If kvm wants full control over the worker thread, kvm can use workqueue as a pure threadpool. Schedule a work item to grab a worker thread with the matching attributes and keep using it as it'd a kthread. While that wouldn't be able to take advantage of work item flushing and so on, it'd still be a simpler way to manage worker threads and the extra stuff like cgroup membership handling doesn't have to be duplicated. > > > opportunity for optimization, at least for some workloads... > > > > What sort of optimizations are we talking about? > > Well, if we take Evlis (1) as for the theoretical base, there could be > benefit of doing I/O scheduling inside the vhost. Yeah, if that actually is beneficial, take full control of the kworker thread. Thanks. -- tejun