[Top][All Lists]
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH 0/3] better I/O accounting
From: |
Christoph Hellwig |
Subject: |
Re: [Qemu-devel] [PATCH 0/3] better I/O accounting |
Date: |
Fri, 12 Aug 2011 15:40:33 +0200 |
User-agent: |
Mutt/1.5.17 (2007-11-01) |
On Fri, Aug 12, 2011 at 06:50:57AM +0100, Stefan Hajnoczi wrote:
> I do see the drawbacks of leaving accounting in block.c on every
> request. For example, we'll fetch the timestamp for internal requests
> as well as external requests from hardware emulation. Due to memory
> mapping and bounce buffers it is also possible that requests get
> split. Multiwrite also changes the I/O pattern.
>
> So I guess this external accounting cookie approach is okay. We just
> need to be strict about reviewing any code that uses bdrv_aio_*() to
> make sure it has accounting in place where appropriate.
The most important point is that we potentially have a lot of
bdrv_aio_read/write calls for a single guest request. That's the case
for both scsi and ide, only virtio does 1 call per guest request (modulo
multiwrite).