From: Kevin Wolf <kwolf@redhat.com>
To: Peter Lieven <pl@kamp.de>
Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, mreitz@redhat.com
Subject: Re: [Qemu-devel] [PATCH V5] qemu-img: align result of is_allocated_sectors
Date: Tue, 10 Jul 2018 17:31:55 +0200 [thread overview]
Message-ID: <20180710153155.GM5852@localhost.localdomain> (raw)
In-Reply-To: <1531235146-6048-1-git-send-email-pl@kamp.de>
Am 10.07.2018 um 17:05 hat Peter Lieven geschrieben:
> We currently don't enforce that the sparse segments we detect during convert are
> aligned. This leads to unnecessary and costly read-modify-write cycles either
> internally in Qemu or in the background on the storage device as nearly all
> modern filesystems or hardware have a 4k alignment internally.
>
> This patch modifies is_allocated_sectors so that its *pnum result will always
> end at an alignment boundary. This way all requests will end at an alignment
> boundary. The start of all requests will also be aligned as long as the results
> of get_block_status do not lead to an unaligned offset.
>
> The number of RMW cycles when converting an example image [1] to a raw device that
> has 4k sector size is about 4600 4k read requests to perform a total of about 15000
> write requests. With this path the additional 4600 read requests are eliminated while
> the number of total write requests stays constant.
>
> [1] https://cloud-images.ubuntu.com/releases/16.04/release/ubuntu-16.04-server-cloudimg-amd64-disk1.vmdk
>
> Signed-off-by: Peter Lieven <pl@kamp.de>
It looked convincing, but I'm afraid this is still not correct.
qemu-iotests 122 fails for me with this patch.
Kevin
next prev parent reply other threads:[~2018-07-10 15:32 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-10 15:05 [Qemu-devel] [PATCH V5] qemu-img: align result of is_allocated_sectors Peter Lieven
2018-07-10 15:31 ` Kevin Wolf [this message]
2018-07-10 20:16 ` Peter Lieven
2018-07-11 8:25 ` Kevin Wolf
2018-07-12 9:23 ` Peter Lieven
2018-07-12 9:26 ` Peter Lieven
2018-07-12 11:41 ` Kevin Wolf
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