linux-kernel - Re: [PATCH RFC] virtio: put last seen used index into ring itself

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Date:	Thu, 6 May 2010 12:01:34 +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: [PATCH RFC] virtio: put last seen used index into ring itself

On Thu, 6 May 2010 06:28:14 am Michael S. Tsirkin wrote:
> Rusty,
> this is a simplified form of a patch you posted in the past.
> I have a vhost patch that, using this feature, shows external
> to host bandwidth grow from 5 to 7 GB/s, by avoiding
> an interrupt in the window after previous interrupt
> was sent and before interrupts were disabled for the vq.
> With vhost under some external to host loads I see
> this window being hit about 30% sometimes.

Fascinating.  So you use this to guess if the guest is still processing?
I haven't thought about it hard, but is that racy?

Obviously happy to apply this when you finalize it.

Thanks!
Rusty.
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