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From: Kevin Wolf <kwolf@redhat.com>
To: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, armbru@redhat.com,
	eblake@redhat.com, fam@euphon.net, stefanha@redhat.com,
	mreitz@redhat.com, pbonzini@redhat.com, den@openvz.org
Subject: Re: [Qemu-devel] [PATCH] block: don't probe zeroes in bs->file by default on block_status
Date: Fri, 11 Jan 2019 11:41:26 +0100	[thread overview]
Message-ID: <20190111104126.GC5010@dhcp-200-186.str.redhat.com> (raw)
In-Reply-To: <20190110132048.49451-1-vsementsov@virtuozzo.com>

Am 10.01.2019 um 14:20 hat Vladimir Sementsov-Ogievskiy geschrieben:
> drv_co_block_status digs bs->file for additional, more accurate search
> for hole inside region, reported as DATA by bs since 5daa74a6ebc.
> 
> This accuracy is not free: assume we have qcow2 disk. Actually, qcow2
> knows, where are holes and where is data. But every block_status
> request calls lseek additionally. Assume a big disk, full of
> data, in any iterative copying block job (or img convert) we'll call
> lseek(HOLE) on every iteration, and each of these lseeks will have to
> iterate through all metadata up to the end of file. It's obviously
> ineffective behavior. And for many scenarios we don't need this lseek
> at all.
> 
> So, let's "5daa74a6ebc" by default, leaving an option to return
> previous behavior, which is needed for scenarios with preallocated
> images.
> 
> Add iotest illustrating new option semantics.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

I still think that an option isn't a good solution and we should try use
some heuristics instead.

Kevin

  parent reply	other threads:[~2019-01-11 10:41 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-10 13:20 [Qemu-devel] [PATCH] block: don't probe zeroes in bs->file by default on block_status Vladimir Sementsov-Ogievskiy
2019-01-10 20:51 ` Eric Blake
2019-01-11  7:54   ` Vladimir Sementsov-Ogievskiy
2019-01-11 10:13     ` Vladimir Sementsov-Ogievskiy
2019-01-11 16:02     ` Eric Blake
2019-01-11 16:05       ` Eric Blake
2019-01-11 16:22       ` Vladimir Sementsov-Ogievskiy
2019-01-11 17:12         ` Eric Blake
2019-01-11 10:41 ` Kevin Wolf [this message]
2019-01-11 11:40   ` Vladimir Sementsov-Ogievskiy
2019-01-11 12:21     ` Kevin Wolf
2019-01-11 12:59       ` Vladimir Sementsov-Ogievskiy
2019-01-11 13:15         ` Kevin Wolf
2019-01-11 16:09           ` Vladimir Sementsov-Ogievskiy
2019-01-11 17:04             ` Eric Blake
2019-01-11 17:27               ` Vladimir Sementsov-Ogievskiy
2019-01-22 18:57     ` Kevin Wolf
2019-01-23 11:53       ` Vladimir Sementsov-Ogievskiy
2019-01-23 16:33         ` Kevin Wolf
2019-01-24 14:36           ` Vladimir Sementsov-Ogievskiy
2019-01-24 15:31             ` Kevin Wolf
2019-01-24 15:47               ` Vladimir Sementsov-Ogievskiy
2019-01-23 12:04       ` Vladimir Sementsov-Ogievskiy
2019-01-24 14:37         ` Vladimir Sementsov-Ogievskiy
2019-01-24 15:39           ` Kevin Wolf
2019-01-24 15:49             ` Eric Blake
2019-01-24 15:53             ` Vladimir Sementsov-Ogievskiy

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