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Re: [Qemu-block] [PATCH] qemu-img: Speed up comparing empty/zero images
From: |
Kevin Wolf |
Subject: |
Re: [Qemu-block] [PATCH] qemu-img: Speed up comparing empty/zero images |
Date: |
Mon, 18 Jan 2016 14:32:13 +0100 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
Am 13.01.2016 um 09:37 hat Fam Zheng geschrieben:
> Two empty raw files are always compared by actually reading data even if
> there is no data, because BDRV_BLOCK_ZERO is considered "allocated" in
> bdrv_is_allocated_above(). That is inefficient.
>
> Use bdrv_get_block_status_above() for more information, and skip the
> consecutive zero sectors.
>
> This brings a huge speed up in comparing sparse/empty raw images:
>
> $ qemu-img create a 1G
>
> $ time ~/build/master/bin/qemu-img compare a a
> Images are identical.
>
> real 0m6.583s
> user 0m0.191s
> sys 0m6.367s
>
> $ time qemu-img compare a a
> Images are identical.
>
> real 0m0.033s
> user 0m0.003s
> sys 0m0.031s
>
> Signed-off-by: Fam Zheng <address@hidden>
Thanks, applied to the block branch.
Kevin