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Re: [Qemu-devel] [PATCHv4] block: optimize zero writes with bdrv_write_z
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [PATCHv4] block: optimize zero writes with bdrv_write_zeroes |
Date: |
Mon, 12 May 2014 14:28:44 -0600 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0 |
On 05/08/2014 10:22 AM, Peter Lieven wrote:
> this patch tries to optimize zero write requests
> by automatically using bdrv_write_zeroes if it is
> supported by the format.
>
> This significantly speeds up file system initialization and
> should speed zero write test used to test backend storage
> performance.
>
> Signed-off-by: Peter Lieven <address@hidden>
> ---
> v3->v4: - use QAPI generated enum and lookup table [Kevin]
> - added more details about the options in the comments
> of the qapi-schema [Eric]
> - changed the type of detect_zeroes from str to
> BlockdevDetectZeroesOptions. I left the name
> as is because it is consistent with e.g.
> BlockdevDiscardOptions or BlockdevAioOptions [Eric]
> - changed the parse function in blockdev_init to
> be generic usable for other enum parameters
If you wouldn't mind, I think the generic function is useful enough that
people might want to backport it independently from this optimization.
It would be better to split this into a two-patch series, one for the
new parse_enum_option, the other for bdrv_write_zeroes utilizing it.
> + },{
> + .name = "detect-zeroes",
> + .type = QEMU_OPT_STRING,
> + .help = "try to optimize zero writes",
Might be worth listing (off, on, unmap) in the text.
Everything else looked okay, but I'll wait for R-b until I see a
response about the idea of splitting the patch (even if that response is
justification for keeping it as one)
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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