From: Avi Kivity <avi@redhat.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Matthew Tippett <tippettm@gmail.com>,
Dustin Kirkland <dustin.kirkland@gmail.com>,
Anthony Liguori <anthony@codemonkey.ws>, RW <kvm@tauceti.net>,
kvm@vger.kernel.org
Subject: Re: sync guest calls made async on host - SQLite performance
Date: Thu, 15 Oct 2009 01:56:40 +0900 [thread overview]
Message-ID: <4AD602C8.4090603@redhat.com> (raw)
In-Reply-To: <20091014134122.GA14235@lst.de>
On 10/14/2009 10:41 PM, Christoph Hellwig wrote:
>> But can't this be also implemented using QUEUE_ORDERED_DRAIN, and on the
>> host side disabling the backing device write cache? I'm talking about
>> cache=none, primarily.
>>
> Yes, it could. But as I found out in a long discussion with Stephen
> it's not actually nessecary. All filesystems do the right thing for
> a device not claiming to support barriers if it doesn't include write
> caches, that is implement ordering internally. So there is no urge to
> set QUEUE_ORDERED_DRAIN for the case without write cache.
>
Does virtio say it has a write cache or not (and how does one say it?)?
According to the report, a write+fdatasync completes too fast, at least
on Ubuntu's qemu. So perhaps somewhere this information is lost.
--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.
next prev parent reply other threads:[~2009-10-14 16:57 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-09-25 7:00 sync guest calls made async on host - SQLite performance RW
2009-09-27 11:37 ` Avi Kivity
2009-09-27 12:07 ` Matthew Tippett
2009-09-29 19:02 ` Anthony Liguori
2009-09-29 19:32 ` Matthew Tippett
2009-09-29 20:46 ` Dustin Kirkland
2009-09-29 20:51 ` Anthony Liguori
2009-10-07 14:15 ` Matthew Tippett
2009-10-07 16:53 ` Matthew Tippett
2009-10-07 18:59 ` Dustin Kirkland
2009-10-07 19:31 ` Matthew Tippett
2009-10-07 20:12 ` Avi Kivity
2009-10-07 21:01 ` Matthew Tippett
2009-10-09 6:05 ` Dustin Kirkland
[not found] ` <4ACE0196.9010904@gmail.com>
[not found] ` <d9c105ea0910082312n7218e1abhc69a2be660838e89@mail.gmail.com>
[not found] ` <f28b49ce0910090425p385636c3he6dfb7595927d7e4@mail.gmail.com>
2009-10-09 15:18 ` Dustin Kirkland
2009-10-09 19:06 ` Matthew Tippett
2009-10-11 9:16 ` Avi Kivity
2009-10-13 22:37 ` Christoph Hellwig
2009-10-14 11:03 ` Avi Kivity
2009-10-14 12:03 ` [PATCH] virtio-blk: fallback to draining the queue if barrier ops are not supported Avi Kivity
2009-10-14 14:46 ` Javier Guerra
2009-10-14 16:53 ` Avi Kivity
2009-10-14 15:38 ` Michael Tokarev
2009-10-14 15:46 ` Christoph Hellwig
2009-10-14 13:41 ` sync guest calls made async on host - SQLite performance Christoph Hellwig
2009-10-14 16:56 ` Avi Kivity [this message]
2009-10-14 17:02 ` Christoph Hellwig
2009-10-14 22:54 ` Anthony Liguori
2009-10-14 23:37 ` Avi Kivity
2009-10-15 12:17 ` Christoph Hellwig
2009-10-15 12:36 ` Christoph Hellwig
2009-10-19 5:56 ` Avi Kivity
2009-10-13 23:08 ` Anthony Liguori
2009-10-14 2:09 ` Matthew Tippett
2009-10-14 4:12 ` Dustin Kirkland
2009-10-14 11:32 ` Matthew Tippett
-- strict thread matches above, loose matches on Subject: below --
2009-09-25 2:11 Ian Woodstock
2009-09-25 3:13 ` Matthew Tippett
2009-09-23 15:58 Matthew Tippett
2009-09-24 11:44 ` Avi Kivity
2009-09-24 12:31 ` Matthew Tippett
2009-09-24 13:03 ` Avi Kivity
2009-09-24 19:49 ` Matthew Tippett
2009-09-25 7:22 ` Avi Kivity
2009-09-25 11:33 ` Matthew Tippett
2009-09-25 15:04 ` Avi Kivity
2009-09-29 18:58 ` Anthony Liguori
2009-09-29 18:57 ` Anthony Liguori
2009-09-29 18:54 ` Anthony Liguori
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