From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH V5 4/5] virtio-scsi: introduce multiqueue support Date: Wed, 20 Mar 2013 10:53:59 +0100 Message-ID: <51498737.8000800@redhat.com> References: <1363687057-13580-1-git-send-email-gaowanlong@cn.fujitsu.com> <1363687057-13580-5-git-send-email-gaowanlong@cn.fujitsu.com> <20130320014657.GA14714@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20130320014657.GA14714@google.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Venkatesh Srinivas Cc: kvm@vger.kernel.org, linux-scsi@vger.kernel.org, mst@redhat.com, linux-kernel@vger.kernel.org, JBottomley@parallels.com, virtualization@lists.linux-foundation.org, vsrinivas@ops101.org, mikew@google.com List-Id: virtualization@lists.linuxfoundation.org Il 20/03/2013 02:46, Venkatesh Srinivas ha scritto: > This looks pretty good! > > I rather like the (lack of) locking in I/O completion (around the req > count vs. target/queue binding). It is unfortunate that you need to hold > the per-target lock in virtscsi_pick_vq() though; have any idea > how much that lock hurts? It doesn't hurt, the lock is mostly uncontended. - if you have lots of I/O, it's held for a very small period of time; if you have little I/O, it's uncontended anyway. - the SCSI layer will serialize on the host lock anyway before calling into the LLD. Locks are "pipelined" so that in the end the host lock will be a bigger bottleneck than the others. Most of the time it only costs 2 extra atomic operations, which should be galf a microsecond or less. Paolo > Just two minor comments: > > (in struct virtio_scsi_target_data): > + /* This spinlock never help at the same time as vq_lock. */ > ^^^^ held? > > (in struct virtio_scsi): > + /* Does the affinity hint is set for virtqueues? */ > Could you rephrase that, please? > > Tested on qemu and w/ Google Compute Engine's virtio-scsi device. > > Reviewed-and-tested-by: Venkatesh Srinivas > > Thanks, > -- vs;