From: Kevin Wolf <kwolf@redhat.com>
To: Christoph Hellwig <hch@lst.de>
Cc: qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [PATCH v3 1/2] Add bdrv_aio_multiwrite
Date: Fri, 11 Sep 2009 08:29:09 +0200 [thread overview]
Message-ID: <4AA9EE35.9020900@redhat.com> (raw)
In-Reply-To: <20090910224401.GB25700@lst.de>
Am 11.09.2009 00:44, schrieb Christoph Hellwig:
> One thing that concerns me here is that we keep adding more memory
> allocations to the I/O path. At least on fast SSDs even kernel memory
> allocations are a performance problem and they're much faster than
> userspace ones.
In the non-merging case we have one additional allocation, the one for
mcb. Maybe we could do something like the AIOPool here to avoid some
mallocs.
In the merging case we need to allocate new IO vectors. I don't see a
way around this, though, and I hope that the benefit of a saved write
request outweighs the malloc costs. If not, it probably was a bad idea
to accept your suggestion to make it generic code instead of just
merging requests for qcow2.
Kevin
next prev parent reply other threads:[~2009-09-11 6:30 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-09-09 15:53 [Qemu-devel] [PATCH v3 0/2] block: Handle multiple write requests at once Kevin Wolf
2009-09-09 15:53 ` [Qemu-devel] [PATCH v3 1/2] Add bdrv_aio_multiwrite Kevin Wolf
[not found] ` <m3ocpj67ip.fsf@neno.mitica>
2009-09-10 7:07 ` [Qemu-devel] " Kevin Wolf
2009-09-10 22:44 ` [Qemu-devel] " Christoph Hellwig
2009-09-11 6:29 ` Kevin Wolf [this message]
2009-09-11 18:36 ` Christoph Hellwig
2009-09-09 15:53 ` [Qemu-devel] [PATCH v3 2/2] virtio-blk: Use bdrv_aio_multiwrite Kevin Wolf
2009-09-10 22:41 ` Christoph Hellwig
2009-09-11 7:10 ` Kevin Wolf
2009-09-11 18:39 ` Christoph Hellwig
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