|
From: | Gerd Hoffmann |
Subject: | Re: [Qemu-devel] buffer alignment for block backends |
Date: | Thu, 09 Apr 2009 17:50:19 +0200 |
User-agent: | Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1b3pre) Gecko/20090324 Fedora/3.0-2.1.beta2.fc11 Thunderbird/3.0b2 |
On 04/09/09 17:21, Samuel Thibault wrote:
Gerd Hoffmann, le Thu 09 Apr 2009 15:54:34 +0200, a écrit :On 04/09/09 15:30, Stefano Stabellini wrote:The userspace\kernelspace distinction does not make much sense in minios, but yes it provides an interface to communicate with blkback in dom0. This interface is used by block-vbd in qemu instead of block-raw-posix when run in minios.Sit back, look again. Do you really need it being page-aligned?Page aligned is an optimization which comes for free when you can already choose the alignment.
Ok, so you don't have to.Does it have an effect positive actually? i.e. do you have requests which would fit into one page but actually span two due to the misalignment?
At least when watching the linux kernel access pattern I see larger requests being page aligned anyway. Probably page cache reads and writes.
The xen block protocol can handle unaligned requests just fine.Not completely arbitrarily aligned requests. They need to be sector-aligned.
Agreed. Sector-alignment you have anyway, thats why I didn't wrote that explicitly.
cheers, Gerd
[Prev in Thread] | Current Thread | [Next in Thread] |