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    SubjectRe: [PATCH 0/5] Add vhost-blk support
    Il 17/07/2012 10:29, Asias He ha scritto:
    > So, vhost-blk at least saves ~6 syscalls for us in each request.

    Are they really 6? If I/O is coalesced by a factor of 3, for example
    (i.e. each exit processes 3 requests), it's really 2 syscalls per request.

    Also, is there anything we can improve? Perhaps we can modify epoll and
    ask it to clear the eventfd for us (would save 2 reads)? Or
    io_getevents (would save 1)?

    > I guess you mean qemu here. Yes, in theory, qemu's block layer can be
    > improved to achieve similar performance as vhost-blk or kvm tool's
    > userspace virito-blk has. But I think it makes no sense to prevent one
    > solution becase there is another in theory solution called: we can do
    > similar in qemu.

    It depends. Like vhost-scsi, vhost-blk has the problem of a crippled
    feature set: no support for block device formats, non-raw protocols,
    etc. This makes it different from vhost-net.

    So it begs the question, is it going to be used in production, or just a
    useful reference tool?

    Paolo


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