From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dor Laor Subject: Re: [PATCH 3/3] virtio-blk: Add bio-based IO path for virtio-blk Date: Tue, 03 Jul 2012 17:28:12 +0300 Message-ID: <4FF3017C.4020605@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> <4FF3001C.9020706@redhat.com> Reply-To: dlaor@redhat.com Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org, "Michael S. Tsirkin" , linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Christoph Hellwig To: Ronen Hod Return-path: In-Reply-To: <4FF3001C.9020706@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 List-Id: kvm.vger.kernel.org On 07/03/2012 05:22 PM, Ronen Hod wrote: > On 06/18/2012 02:14 PM, 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. > > Does it make sense to use the guest's I/O scheduler at all? That's the reason we have a noop io scheduler. > - It is not aware of the physical (spinning) disk layout. > - It is not aware of all the host's disk pending requests. > It does have a good side-effect - batching of requests. > > Ronen. > >> >>> >>> Cheers, >>> Rusty. >>> _______________________________________________ >>> Virtualization mailing list >>> Virtualization@lists.linux-foundation.org >>> https://lists.linuxfoundation.org/mailman/listinfo/virtualization >> >> -- >> To unsubscribe from this list: send the line "unsubscribe kvm" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html >