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Date: Mon, 01 Jun 2015 13:26:28 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v5 0/2] block: enforce minimal 4096
	alignment in qemu_blockalign
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To: Dmitry Monakhov <dmonakhov@openvz.org>, "Denis V. Lunev" <den@odin.com>, Stefan Hajnoczi <stefanha@gmail.com>
Cc: Dmitry Monakhov <dmonakhov@odin.com>, Stefan Hajnoczi <stefanha@redhat.com>, qemu-block@nongnu.org, qemu-devel@nongnu.org



On 01/06/2015 13:16, Dmitry Monakhov wrote:
> 259,0   31      385     0.719283423 10729  Q  WS 29376775 + 248 [qemu-i=
o]
> 259,0   31      388     0.719287600 10729  Q  WS 29377023 + 8 [qemu-io]
> 259,0   31      391     0.719315193 10729  Q  WS 29377031 + 248 [qemu-i=
o]
> 259,0   31      394     0.719319179 10729  Q  WS 29377279 + 8 [qemu-io]

Compared to the old one:

>    9,0   11        1     0.000000000 11151  Q  WS 312737792 + 1023 [qem=
u-img]
>    9,0   11        2     0.000007938 11151  Q  WS 312738815 + 8 [qemu-i=
mg]
>    9,0   11        3     0.000030735 11151  Q  WS 312738823 + 1016 [qem=
u-img]
>    9,0   11        4     0.000032482 11151  Q  WS 312739839 + 8 [qemu-i=
mg]
>    9,0   11        5     0.000041379 11151  Q  WS 312739847 + 1016 [qem=
u-img]
>    9,0   11        6     0.000042818 11151  Q  WS 312740863 + 8 [qemu-i=
mg]
>    9,0   11        7     0.000051236 11151  Q  WS 312740871 + 1017 [qem=
u-img]

I suspect the difference is that my patch avoids RMW operations on disks
that have 512-byte logical blocks and 4K physical blocks.

Paolo