linux-kernel - Re: [PATCHv2-RFC 0/2] virtio: put last seen used index into ring itself

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Message-Id: <201005311716.43573.rusty@rustcorp.com.au>
Date:	Mon, 31 May 2010 17:16:42 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
	qemu-devel@...gnu.org
Subject: Re: [PATCHv2-RFC 0/2] virtio: put last seen used index into ring itself

On Thu, 27 May 2010 05:20:35 am Michael S. Tsirkin wrote:
> Here's a rewrite of the original patch with a new layout.
> I haven't tested it yet so no idea how this performs, but
> I think this addresses the cache bounce issue raised by Avi.
> Posting for early flames/comments.

Sorry, not without some evidence that it'll actually reduce cacheline
bouncing.  I *think* it will, but it's not obvious: the host may keep
looking at avail_idx as we're updating last_seen.  Or does qemu always
look at both together anyway?

Can someone convince me this is a win?
Rusty.
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