Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752284Ab2FRLil (ORCPT ); Mon, 18 Jun 2012 07:38:41 -0400 Received: from mail-ob0-f174.google.com ([209.85.214.174]:42237 "EHLO mail-ob0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751270Ab2FRLik (ORCPT ); Mon, 18 Jun 2012 07:38:40 -0400 Message-ID: <1340019575.22848.2.camel@lappy> Subject: Re: [PATCH 3/3] virtio-blk: Add bio-based IO path for virtio-blk From: Sasha Levin To: dlaor@redhat.com Cc: Rusty Russell , Asias He , kvm@vger.kernel.org, "Michael S. Tsirkin" , linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Christoph Hellwig Date: Mon, 18 Jun 2012 13:39:35 +0200 In-Reply-To: <4FDF0DA7.40604@redhat.com> 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> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3 Content-Transfer-Encoding: 7bit Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1315 Lines: 28 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? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/