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    SubjectRe: BTRFS: Unbelievably slow with kvm/qemu
    On Mon, Jul 12, 2010 at 03:34:44PM +0200, Giangiacomo Mariotti wrote:
    > On Mon, Jul 12, 2010 at 9:09 AM, Michael Tokarev <mjt@tls.msk.ru> wrote:
    > >
    > > This looks quite similar to a problem with ext4 and O_SYNC which I
    > > reported earlier but no one cared to answer (or read?) - there:
    > > http://permalink.gmane.org/gmane.linux.file-systems/42758
    > > (sent to qemu-devel and linux-fsdevel lists - Cc'd too).  You can
    > > try a few other options, esp. cache=none and re-writing some guest
    > > files to verify.
    > >
    > > /mjt
    > >
    > Either way, changing to cache=none I suspect wouldn't tell me much,
    > because if it's as slow as before, it's still unusable and if instead
    > it's even slower, well it'd be even more unusable, so I wouldn't be
    > able to tell the difference. What I can say for certain is that with
    > the exact same virtual hd file, same options, same system, but on an
    > ext3 fs there's no problem at all, on a Btrfs is not just slower, it
    > takes ages.
    >

    O_DIRECT support was just introduced recently, please try on the latest kernel
    with the normal settings (which IIRC uses O_DIRECT), that should make things
    suck alot less. Thanks,

    Josef
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