linux-kernel - Re: [PATCH] virtio-ring: Use threshold for switching to indirect descriptors

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Message-ID: <4ED4F30F.8000603@redhat.com>
Date:	Tue, 29 Nov 2011 16:58:23 +0200
From:	Avi Kivity <avi@...hat.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
CC:	Sasha Levin <levinsasha928@...il.com>,
	linux-kernel@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
	markmc@...hat.com
Subject: Re: [PATCH] virtio-ring: Use threshold for switching to indirect
 descriptors

On 11/29/2011 04:54 PM, Michael S. Tsirkin wrote:
> > 
> > Which is actually strange, weren't indirect buffers introduced to make
> > the performance *better*? From what I see it's pretty much the
> > same/worse for virtio-blk.
>
> I know they were introduced to allow adding very large bufs.
> See 9fa29b9df32ba4db055f3977933cd0c1b8fe67cd
> Mark, you wrote the patch, could you tell us which workloads
> benefit the most from indirect bufs?
>

Indirects are really for block devices with many spindles, since there
the limiting factor is the number of requests in flight.  Network
interfaces are limited by bandwidth, it's better to increase the ring
size and use direct buffers there (so the ring size more or less
corresponds to the buffer size).

-- 
error compiling committee.c: too many arguments to function

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