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

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Date:	Sun, 04 Dec 2011 19:39:34 +0200
From:	Sasha Levin <levinsasha928@...il.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	"Michael S. Tsirkin" <mst@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	linux-kernel@...r.kernel.org,
	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 Sun, 2011-12-04 at 19:37 +0200, Avi Kivity wrote:
> On 12/04/2011 07:34 PM, Sasha Levin wrote:
> > > 
> > > I'm confused. didn't you see a bigger benefit for guest->host by
> > > switching indirect off?
> >
> > The 5% improvement is over the 'regular' indirect on, not over indirect
> > off. Sorry for the confusion there.
> >
> > I suggested this change regardless of the outcome of indirect descriptor
> > threshold discussion, since it would help anyways.
> 
> For net, this makes sense.  For block, it reduces the effective queue
> depth, so it's not a trivial change.  It probably makes sense there too,
> though.

It doesn't have to be limited at that number, anything above that can go
through the regular kmalloc() path.

-- 

Sasha.

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