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    SubjectRe: [PATCH 0/6][RFC] virtio-blk: Change I/O path from request to BIO
    On Thu, Dec 22, 2011 at 12:57:40PM +0000, Stefan Hajnoczi wrote:
    > On Wed, Dec 21, 2011 at 1:00 AM, Minchan Kim <> wrote:
    > > This patch is follow-up of Christohp Hellwig's work
    > > [RFC: ->make_request support for virtio-blk].
    > >
    > >
    > > Quote from hch
    > > "This patchset allows the virtio-blk driver to support much higher IOP
    > > rates which can be driven out of modern PCI-e flash devices.  At this
    > > point it really is just a RFC due to various issues."
    > Basic question to make sure I understood this series: does this patch
    > bypass the guest I/O scheduler (but then you added custom batching
    > code into virtio_blk.c)?


    > If you're stumped by the performance perhaps compare blktraces of the
    > request approach vs the bio approach. We're probably performing I/O
    > more CPU-efficiently but the I/O pattern itself is worse.

    You mean I/O scheduler have many techniques to do well in I/O pattern?
    That's what I want to discuss in this RFC.

    I guess request layer have many techniques proved during long time
    to do well I/O but BIO-based drvier ignores them for just reducing locking
    overhead. Of course, we can add such techniques to BIO-batch driver like
    custom-batch in this series. But it needs lots of work, is really duplication,
    and will have a problem on maintenance.

    I would like to listen opinions whether this direction is good or bad.

    > Stefan

    Kind regards,
    Minchan Kim
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