From: Christoph Hellwig <hch@lst.de>
To: Stefan Hajnoczi <stefanha@gmail.com>
Cc: Christoph Hellwig <hch@lst.de>, qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [PATCH 0/3] better I/O accounting
Date: Fri, 12 Aug 2011 15:40:33 +0200 [thread overview]
Message-ID: <20110812134033.GA31736@lst.de> (raw)
In-Reply-To: <CAJSP0QW08wAbrM4EMyDgQpJtzaEOa0H9WGC4U2ei+bhQ0CCEXQ@mail.gmail.com>
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).
prev parent reply other threads:[~2011-08-12 13:40 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-08-11 23:44 [Qemu-devel] [PATCH 0/3] better I/O accounting Christoph Hellwig
2011-08-11 23:44 ` [Qemu-devel] [PATCH 1/3] block: include flush requests in info blockstats Christoph Hellwig
2011-08-11 23:44 ` [Qemu-devel] [PATCH 2/3] block: explicit I/O accounting Christoph Hellwig
2011-08-11 23:44 ` [Qemu-devel] [PATCH 3/3] block: latency accounting Christoph Hellwig
2011-08-12 5:14 ` [Qemu-devel] [PATCH 0/3] better I/O accounting Stefan Hajnoczi
2011-08-12 5:50 ` Stefan Hajnoczi
2011-08-12 13:40 ` Christoph Hellwig [this message]
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