From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sasha Levin Subject: Re: [PATCH 3/3] virtio-blk: Add bio-based IO path for virtio-blk Date: Mon, 18 Jun 2012 13:39:35 +0200 Message-ID: <1340019575.22848.2.camel@lappy> References: <1340002390-3950-1-git-send-email-asias@redhat.com> <1340002390-3950-4-git-send-email-asias@redhat.com> <87hau9yse7.fsf@rustcorp.com.au> <4FDEE0CB.1030505@redhat.com> <87zk81x7dp.fsf@rustcorp.com.au> <4FDF0DA7.40604@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4FDF0DA7.40604@redhat.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: dlaor@redhat.com Cc: kvm@vger.kernel.org, "Michael S. Tsirkin" , linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Christoph Hellwig List-Id: virtualization@lists.linuxfoundation.org On Mon, 2012-06-18 at 14:14 +0300, Dor Laor wrote: > On 06/18/2012 01:05 PM, Rusty Russell wrote: > > On Mon, 18 Jun 2012 16:03:23 +0800, Asias He wrote: > >> On 06/18/2012 03:46 PM, Rusty Russell wrote: > >>> On Mon, 18 Jun 2012 14:53:10 +0800, Asias He wrote: > >>>> This patch introduces bio-based IO path for virtio-blk. > >>> > >>> Why make it optional? > >> > >> request-based IO path is useful for users who do not want to bypass the > >> IO scheduler in guest kernel, e.g. users using spinning disk. For users > >> using fast disk device, e.g. SSD device, they can use bio-based IO path. > > > > Users using a spinning disk still get IO scheduling in the host though. > > What benefit is there in doing it in the guest as well? > > The io scheduler waits for requests to merge and thus batch IOs > together. It's not important w.r.t spinning disks since the host can do > it but it causes much less vmexits which is the key issue for VMs. Is the amount of exits caused by virtio-blk significant at all with EVENT_IDX?