linux-kernel - Re: [PATCH] virtio-net: fix a race on 32bit arches

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Date:	Wed, 6 Jun 2012 23:19:43 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Jason Wang <jasowang@...hat.com>, netdev@...r.kernel.org,
	rusty@...tcorp.com.au, linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	Stephen Hemminger <shemminger@...tta.com>
Subject: Re: [PATCH] virtio-net: fix a race on 32bit arches

On Wed, Jun 06, 2012 at 10:06:11PM +0200, Eric Dumazet wrote:
> On Wed, 2012-06-06 at 21:43 +0300, Michael S. Tsirkin wrote:
> 
> > 1. We are trying to look at counters for purposes of tuning the device.
> > E.g. if ethtool reports packets and bytes, we'd like to calculate
> > average packet size by bytes/packets.
> > 
> > If both counters are read atomically the metric becomes more exact.
> > Not a must but nice to have.
> > 
> 
> metrics are exact right now.

Yes, but they are not synchronised between themselves.
E.g. you can in theory have a report where #of packets > #of bytes.

I know there's no guarantee they are synchronised
on an arbitrary device but if they are, without
slowing fast path, it's nice.
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