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: [Qemu-devel] [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 10:02 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-10-03 22:05 [Qemu-devel] [PATCH 0/4] Improve emulated scsi write performance Ryan Harper
2008-10-03 22:05 ` [Qemu-devel] [PATCH 1/4] lsi_queue_command: add dma direction parameter Ryan Harper
2008-10-03 22:05 ` [Qemu-devel] [PATCH 2/4] Refactor lsi_do_command to queue read and write ops Ryan Harper
2008-10-03 22:05 ` [Qemu-devel] [PATCH 3/4] Refactor scsi-disk layer for queue'ing writes Ryan Harper
2008-10-03 22:05 ` [Qemu-devel] [PATCH 4/4] Reallocate dma buffers in read/write path if needed Ryan Harper
2008-10-03 23:17 ` 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
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