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[109.67.54.78]) by smtp.gmail.com with ESMTPSA id o13sm2811565wmc.44.2020.11.18.01.54.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 18 Nov 2020 01:54:10 -0800 (PST) Date: Wed, 18 Nov 2020 04:54:07 -0500 From: "Michael S. Tsirkin" To: Mike Christie Subject: Re: [PATCH 00/10] vhost/qemu: thread per IO SCSI vq Message-ID: <20201118044620-mutt-send-email-mst@kernel.org> References: <1605223150-10888-1-git-send-email-michael.christie@oracle.com> <20201117164043.GS131917@stefanha-x1.localdomain> MIME-Version: 1.0 In-Reply-To: Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mst@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/11/18 00:38:29 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: fam@euphon.net, linux-scsi@vger.kernel.org, jasowang@redhat.com, qemu-devel@nongnu.org, virtualization@lists.linux-foundation.org, target-devel@vger.kernel.org, Stefan Hajnoczi , pbonzini@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Nov 17, 2020 at 01:13:14PM -0600, Mike Christie wrote: > On 11/17/20 10:40 AM, Stefan Hajnoczi wrote: > > On Thu, Nov 12, 2020 at 05:18:59PM -0600, Mike Christie wrote: > >> The following kernel patches were made over Michael's vhost branch: > >> > >> https://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost.git/log/?h=vhost > >> > >> and the vhost-scsi bug fix patchset: > >> > >> https://lore.kernel.org/linux-scsi/20201112170008.GB1555653@stefanha-x1.localdomain/T/#t > >> > >> And the qemu patch was made over the qemu master branch. > >> > >> vhost-scsi currently supports multiple queues with the num_queues > >> setting, but we end up with a setup where the guest's scsi/block > >> layer can do a queue per vCPU and the layers below vhost can do > >> a queue per CPU. vhost-scsi will then do a num_queue virtqueues, > >> but all IO gets set on and completed on a single vhost-scsi thread. > >> After 2 - 4 vqs this becomes a bottleneck. > >> > >> This patchset allows us to create a worker thread per IO vq, so we > >> can better utilize multiple CPUs with the multiple queues. It > >> implments Jason's suggestion to create the initial worker like > >> normal, then create the extra workers for IO vqs with the > >> VHOST_SET_VRING_ENABLE ioctl command added in this patchset. > > > > How does userspace find out the tids and set their CPU affinity? > > > > When we create the worker thread we add it to the device owner's cgroup, > so we end up inheriting those settings like affinity. > > However, are you more asking about finer control like if the guest is > doing mq, and the mq hw queue is bound to cpu0, it would perform > better if we could bind vhost vq's worker thread to cpu0? I think the > problem might is if you are in the cgroup then we can't set a specific > threads CPU affinity to just one specific CPU. So you can either do > cgroups or not. Something we wanted to try for a while is to allow userspace to create threads for us, then specify which vqs it processes. That would address this set of concerns ... -- MST