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Re: [Qemu-devel] [PATCH 5/9] mirror: improve performance of mirroring of

From: Denis V. Lunev
Subject: Re: [Qemu-devel] [PATCH 5/9] mirror: improve performance of mirroring of empty disk
Date: Wed, 15 Jun 2016 13:37:18 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1

On 06/15/2016 12:19 PM, Stefan Hajnoczi wrote:
On Tue, Jun 14, 2016 at 09:20:47PM -0600, Eric Blake wrote:
On 06/14/2016 09:25 AM, Denis V. Lunev wrote:
We should not take into account zero blocks for delay calculations.
They are not read and thus IO throttling is not required. In the
other case VM migration with 16 Tb QCOW2 disk with 4 Gb of data takes

Signed-off-by: Denis V. Lunev <address@hidden>
Reviewed-by: Vladimir Sementsov-Ogievskiy <address@hidden>
CC: Stefan Hajnoczi <address@hidden>
CC: Fam Zheng <address@hidden>
CC: Kevin Wolf <address@hidden>
CC: Max Reitz <address@hidden>
CC: Jeff Cody <address@hidden>
CC: Eric Blake <address@hidden>
  block/mirror.c | 7 +++++--
  1 file changed, 5 insertions(+), 2 deletions(-)
Seems reasonable, but I'll let others more familiar with throttling give
the final say.
There is a bounce buffer fallback when !drv->bdrv_co_pwrite_zeroes.  In
that case we need to account for the bytes transferred.  I don't see
where the patch takes this into account.
Interesting point.

I think we are charging for IO performed. Thus with the
absence of the callback we should charge for io_sectors/2
The write will be full scale, there is no reading.


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