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

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Message-ID: <4EDBA0F0.4000907@redhat.com>
Date:	Sun, 04 Dec 2011 18:33:52 +0200
From:	Avi Kivity <avi@...hat.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
CC:	Sasha Levin <levinsasha928@...il.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 12/04/2011 06:00 PM, Michael S. Tsirkin wrote:
> >  If you
> > copy descriptors, then it goes away.
>
> The avail ring could go away. used could if we make descriptors
> writeable. IIUC it was made RO in the hope that will make it
> easier for xen to adopt. Still relevant?

You mean RO from the consumer side?  Why can't Xen do that?

> > That does suck.  Are there issues in increasing the ring size?  Or
> > making it discontiguous?
>
> discontiguous ring is what indirect is, basically.

No, discontiguous is more cache and prefetch friendly.  With vmap(), the
code doesn't even change.


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

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