From: Christoph Hellwig <hch@lst.de>
To: Kevin Wolf <kwolf@redhat.com>
Cc: qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [PATCH 0/3] block: Handle multiple write requests at once
Date: Tue, 1 Sep 2009 17:52:28 +0200 [thread overview]
Message-ID: <20090901155228.GA21781@lst.de> (raw)
In-Reply-To: <1251813112-17408-1-git-send-email-kwolf@redhat.com>
On Tue, Sep 01, 2009 at 03:51:49PM +0200, Kevin Wolf wrote:
> virtio often issues multiple requests in a row, but each one independently. If
> the block drivers knew all of the requests, they could optimize the way they
> handle the requests. See the description of patch 3 for how qcow2 can use this
> to avoid unnecessary writes to the disk.
I think this interface is extremly awkward and the layering is wrong.
Everyone benefits from having one large instead of multiple small
requests, so if we do get multiple sequential write requests we should
always merged it at a high level even before starting to issue AIO,
e.g. do it all in virtio-blk.
Of course using a sane filesystem in the guest would also fix it,
but the point of virtualization is at least partially to keep all
that old crap working nicely.
next prev parent reply other threads:[~2009-09-01 15:52 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-09-01 13:51 [Qemu-devel] [PATCH 0/3] block: Handle multiple write requests at once Kevin Wolf
2009-09-01 13:51 ` [Qemu-devel] [PATCH 1/3] Add bdrv_aio_multiwrite Kevin Wolf
2009-09-01 13:51 ` [Qemu-devel] [PATCH 2/3] virtio-blk: Use bdrv_aio_multiwrite Kevin Wolf
2009-09-01 13:51 ` [Qemu-devel] [PATCH 3/3] qcow2: Add bdrv_aio_multiwrite implementation Kevin Wolf
2009-09-01 15:52 ` Christoph Hellwig [this message]
2009-09-01 16:08 ` [Qemu-devel] [PATCH 0/3] block: Handle multiple write requests at once Anthony Liguori
2009-09-01 16:14 ` Christoph Hellwig
2009-09-01 17:00 ` Avi Kivity
2009-09-01 16:59 ` Avi Kivity
2009-09-02 7:27 ` Kevin Wolf
2009-09-02 15:43 ` Christoph Hellwig
2009-09-02 15:50 ` Kevin Wolf
2009-09-02 17:26 ` Christoph Hellwig
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