From: Paolo Bonzini <pbonzini@redhat.com>
To: Stefan Weil <sw@weilnetz.de>, phoeagon <phoeagon@gmail.com>,
Kevin Wolf <kwolf@redhat.com>, Max Reitz <mreitz@redhat.com>
Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org
Subject: Re: [Qemu-devel] [PATCH v4] block/vdi: Use bdrv_flush after metadata updates
Date: Sun, 10 May 2015 18:10:08 +0200 [thread overview]
Message-ID: <554F82E0.2000005@redhat.com> (raw)
In-Reply-To: <554F8117.1070800@weilnetz.de>
On 10/05/2015 18:02, Stefan Weil wrote:
>> Since the default qemu-img convert case isn't slowed down, I
>> would think that correctness trumps performance. Nevertheless,
>> it's a huge difference.
>
> I doubt that the convert case isn't slowed down.
The *default* convert case isn't slowed down because "qemu-img convert"
defaults to the "unsafe" cache mode.
The *non-default* convert case with flushes was slowed down indeed: 2x
in total (if you include the final flush done by bdrv_close), and 10x if
you only consider the sequential write part of convert.
Paolo
> Writing to a tmpfs as it was obviously done for the test is not a
> typical use case.
> With real hard disks I expect a significant slowdown.
>
> Stefan
next prev parent reply other threads:[~2015-05-10 16:10 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-05-07 4:04 [Qemu-devel] [PATCH v3] block/vdi: Use bdrv_flush after metadata updates Zhe Qiu
2015-05-07 10:09 ` Stefan Hajnoczi
2015-05-07 15:05 ` [Qemu-devel] [Qemu-block] " Eric Blake
2015-05-07 15:16 ` [Qemu-devel] [PATCH v4] " Zhe Qiu
2015-05-08 13:14 ` Max Reitz
2015-05-08 13:55 ` Kevin Wolf
2015-05-08 14:43 ` phoeagon
2015-05-08 21:26 ` Stefan Weil
2015-05-09 3:54 ` phoeagon
2015-05-09 3:59 ` phoeagon
2015-05-09 6:39 ` Stefan Weil
2015-05-09 7:41 ` phoeagon
2015-05-10 15:01 ` Paolo Bonzini
2015-05-10 16:02 ` Stefan Weil
2015-05-10 16:05 ` phoeagon
2015-05-10 16:10 ` Paolo Bonzini [this message]
2015-05-10 16:26 ` Stefan Weil
2015-05-10 17:14 ` phoeagon
2015-05-08 10:43 ` [Qemu-devel] [Qemu-block] [PATCH v3] " Kevin Wolf
2015-05-08 11:50 ` phoeagon
2015-05-08 12:02 ` Kevin Wolf
2015-05-08 12:56 ` phoeagon
2015-05-08 13:10 ` [Qemu-devel] " Max Reitz
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