linux-kernel - Re: [RFC PATCH]vhost-blk: In-kernel accelerator for virtio block device

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Message-ID: <CAJSP0QUbZ=RAkn_kbDupeA9QYYnzGd+u5M2duEg==e8ACjAqXg@mail.gmail.com>
Date:	Fri, 29 Jul 2011 13:50:52 +0100
From:	Stefan Hajnoczi <stefanha@...il.com>
To:	Liu Yuan <namei.unix@...il.com>
Cc:	"Michael S. Tsirkin" <mst@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Avi Kivity <avi@...hat.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, Khoa Huynh <khoa@...ibm.com>,
	Badari Pulavarty <pbadari@...ibm.com>,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [RFC PATCH]vhost-blk: In-kernel accelerator for virtio block device

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
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