From: Anthony Liguori <anthony@codemonkey.ws>
To: Christoph Hellwig <hch@lst.de>
Cc: Kevin Wolf <kwolf@redhat.com>, qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [PATCH 0/3] block: Handle multiple write requests at once
Date: Tue, 01 Sep 2009 11:08:10 -0500 [thread overview]
Message-ID: <4A9D46EA.8090606@codemonkey.ws> (raw)
In-Reply-To: <20090901155228.GA21781@lst.de>
Christoph Hellwig wrote:
> 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.
>
Or introduce a helper layer that coalesces requests that lives outside
of the core block API.
I don't like the interface either although I'm not sure if the
alternative is better. A different way to do this would be to have a
queuing API. A device would queue requests and then kick the queue.
This is closer to how virtio-blk works.
Regards,
Anthony Liguori
next prev parent reply other threads:[~2009-09-01 16:08 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 ` [Qemu-devel] [PATCH 0/3] block: Handle multiple write requests at once Christoph Hellwig
2009-09-01 16:08 ` Anthony Liguori [this message]
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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