Messages in this thread | | | Date | Tue, 03 Jul 2012 17:28:12 +0300 | From | Dor Laor <> | Subject | Re: [PATCH 3/3] virtio-blk: Add bio-based IO path for virtio-blk |
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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<asias@redhat.com> wrote: >>>> On 06/18/2012 03:46 PM, Rusty Russell wrote: >>>>> On Mon, 18 Jun 2012 14:53:10 +0800, Asias He<asias@redhat.com> 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 >
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