From: Avi Kivity <avi@redhat.com>
To: qemu-devel@nongnu.org
Cc: Anthony Liguori <aliguori@us.ibm.com>,
Ryan Harper <ryanh@us.ibm.com>,
Paul Brook <paul@codesourcery.com>,
kvm@vger.kernel.org
Subject: Re: [PATCH 4/4] Reallocate dma buffers in read/write path if needed
Date: Sat, 04 Oct 2008 13:00:45 +0300 [thread overview]
Message-ID: <48E73ECD.9080309@redhat.com> (raw)
In-Reply-To: <48E6AC36.3060404@codemonkey.ws>
Anthony Liguori wrote:
> Paul Brook wrote:
>> On Friday 03 October 2008, Ryan Harper wrote:
>>
>>> The default buffer size breaks up larger read/write requests
>>> unnecessarily.
>>> When we encounter requests larger than the default dma buffer,
>>> reallocate
>>> the buffer to support the request.
>>>
>>
>> Allocating unboundedly large host buffers based on guest input seems
>> like a bad idea.
>>
>
> Perhaps they could be at least bound to phys_ram_size.
>
So the guest could double the memory load on the host with just one
request?!
> In general, I don't think there's a correct size to bound them that's
> less than phys_ram_size. The guest may be issuing really big IO
> requests.
The correct fix is not to buffer at all but use scatter-gather. Until
this is done buffering has to be bounded.
--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.
next prev parent reply other threads:[~2008-10-04 10:00 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-10-03 22:05 [PATCH 0/4] Improve emulated scsi write performance Ryan Harper
2008-10-03 22:05 ` [PATCH 1/4] lsi_queue_command: add dma direction parameter Ryan Harper
2008-10-03 22:05 ` [PATCH 2/4] Refactor lsi_do_command to queue read and write ops Ryan Harper
2008-10-03 22:05 ` [PATCH 3/4] Refactor scsi-disk layer for queue'ing writes Ryan Harper
2008-10-03 22:05 ` [PATCH 4/4] Reallocate dma buffers in read/write path if needed Ryan Harper
2008-10-03 23:17 ` [Qemu-devel] " Paul Brook
2008-10-03 23:35 ` Anthony Liguori
2008-10-04 0:00 ` Paul Brook
2008-10-04 10:00 ` Avi Kivity [this message]
[not found] ` <20081004135749.pphehrhuw9w4gwsc@imap.linux.ibm.com>
2008-10-04 21:47 ` Ryan Harper
2008-10-04 22:22 ` Anthony Liguori
2008-10-05 5:23 ` Avi Kivity
2008-10-05 23:06 ` Ryan Harper
2008-10-06 7:27 ` Avi Kivity
2008-10-04 23:00 ` Paul Brook
2008-10-05 5:29 ` Avi Kivity
2008-10-05 23:08 ` [Qemu-devel] [PATCH 0/4] Improve emulated scsi write performance Ryan Harper
2008-10-13 16:15 ` Ryan Harper
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=48E73ECD.9080309@redhat.com \
--to=avi@redhat.com \
--cc=aliguori@us.ibm.com \
--cc=kvm@vger.kernel.org \
--cc=paul@codesourcery.com \
--cc=qemu-devel@nongnu.org \
--cc=ryanh@us.ibm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.