From: Liu Yuan <namei.unix@gmail.com>
To: Stefan Hajnoczi <stefanha@gmail.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>,
Rusty Russell <rusty@rustcorp.com.au>,
Avi Kivity <avi@redhat.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Khoa Huynh <khoa@us.ibm.com>,
Badari Pulavarty <pbadari@us.ibm.com>,
Christoph Hellwig <hch@infradead.org>
Subject: Re: [RFC PATCH]vhost-blk: In-kernel accelerator for virtio block device
Date: Fri, 29 Jul 2011 22:50:04 +0800 [thread overview]
Message-ID: <4E32C89C.4010609@gmail.com> (raw)
In-Reply-To: <4E32C79A.80606@gmail.com>
On 07/29/2011 10:45 PM, Liu Yuan wrote:
> On 07/29/2011 08:50 PM, Stefan Hajnoczi wrote:
>> I hit a weirdness yesterday, just want to mention it in case you
>> notice it too.
>>
>> When running vanilla qemu-kvm I forgot to use aio=native. When I
>> compared the results against virtio-blk-data-plane (which *always*
>> uses Linux AIO) I was surprised to find average 4k read latency was
>> lower and the standard deviation was also lower.
>>
>> So from now on I will run tests both with and without aio=native.
>> aio=native should be faster and if I can reproduce the reverse I'll
>> try to figure out why.
>>
>> Stefan
> On my laptop, I don't meet this weirdo. the emulated POSIX AIO is much
> worse than the Linux AIO as expected. If iodepth goes deeper, the gap
> gets wider.
>
> If not set aio=none, qemu uses emulated posix aio interface to do the
> IO. I peek at the posix-aio-compat.c,it uses thread pool and sync
> preadv/pwritev to emulate the AIO behaviour. The sync IO interface
> would even cause much poorer performance for random rw, since
> io-scheduler would possibly never get a chance to merge the requests
> stream. (blk_finish_plug->queue_unplugged->__blk_run_queue)
>
> Yuan
Typo. not merge, I mean *sort* the reqs
next prev parent reply other threads:[~2011-07-29 14:50 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-07-28 14:29 [RFC PATCH]vhost-blk: In-kernel accelerator for virtio block device Liu Yuan
2011-07-28 14:29 ` [RFC PATCH] vhost-blk: An in-kernel accelerator for virtio-blk Liu Yuan
2011-07-28 14:47 ` Christoph Hellwig
2011-07-29 11:19 ` Liu Yuan
2011-07-28 15:18 ` Stefan Hajnoczi
2011-07-28 15:22 ` Michael S. Tsirkin
2011-07-29 15:09 ` Liu Yuan
2011-08-01 6:25 ` Liu Yuan
2011-08-01 8:12 ` Michael S. Tsirkin
2011-08-01 8:55 ` Liu Yuan
2011-08-01 10:26 ` Michael S. Tsirkin
2011-08-11 19:59 ` Dongsu Park
2011-08-12 8:56 ` Alan Cox
2011-07-28 14:29 ` [RFC PATCH] vhost: Enable vhost-blk support Liu Yuan
2011-07-28 15:44 ` [RFC PATCH]vhost-blk: In-kernel accelerator for virtio block device Stefan Hajnoczi
2011-07-29 4:48 ` Stefan Hajnoczi
2011-07-29 7:59 ` Liu Yuan
2011-07-29 10:55 ` Christoph Hellwig
2011-07-29 7:22 ` Liu Yuan
2011-07-29 9:06 ` Stefan Hajnoczi
2011-07-29 12:01 ` Liu Yuan
2011-07-29 12:29 ` Stefan Hajnoczi
2011-07-29 12:50 ` Stefan Hajnoczi
2011-07-29 14:45 ` Liu Yuan
2011-07-29 14:50 ` Liu Yuan [this message]
2011-07-29 15:25 ` Sasha Levin
2011-08-01 8:17 ` Avi Kivity
2011-08-01 9:18 ` Liu Yuan
2011-08-01 9:37 ` Avi Kivity
2011-07-29 18:12 ` Badari Pulavarty
2011-08-01 5:46 ` Liu Yuan
2011-08-01 8:12 ` Christoph Hellwig
2011-08-04 21:58 ` Badari Pulavarty
2011-08-05 7:56 ` Liu Yuan
2011-08-05 11:04 ` Liu Yuan
2011-08-05 18:02 ` Badari Pulavarty
2011-08-08 1:35 ` Liu Yuan
2011-08-08 5:04 ` Badari Pulavarty
2011-08-08 7:31 ` Liu Yuan
2011-08-08 17:16 ` Badari Pulavarty
2011-08-10 2:19 ` Liu Yuan
2011-08-10 20:37 ` Badari Pulavarty
2011-08-11 3:01 ` Liu Yuan
2011-08-11 3:19 ` Liu Yuan
2011-08-11 23:51 ` Badari Pulavarty
2011-08-12 4:50 ` Badari Pulavarty
2011-08-12 6:46 ` Dongsu Park
2011-08-12 8:27 ` Liu Yuan
2011-08-12 11:40 ` Liu Yuan
2011-08-12 16:12 ` Badari Pulavarty
2011-08-15 3:20 ` Liu Yuan
2011-08-15 4:17 ` Badari Pulavarty
2011-08-16 5:44 ` Liu Yuan
2011-09-07 13:36 ` Liu Yuan
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