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

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Date:	Wed, 6 Jun 2012 08:14:32 -0700
From:	Stephen Hemminger <shemminger@...tta.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Jason Wang <jasowang@...hat.com>, netdev@...r.kernel.org,
	rusty@...tcorp.com.au, linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH] virtio-net: fix a race on 32bit arches

On Wed, 6 Jun 2012 17:49:42 +0300
"Michael S. Tsirkin" <mst@...hat.com> wrote:

> Sounds good, but I have a question: this realies on counters
> being atomic on 64 bit.
> Would not it be better to always use a seqlock even on 64 bit?
> This way counters would actually be correct and in sync.
> As it is if we want e.g. average packet size,
> we can not rely e.g. on it being bytes/packets.

This has not been a requirement on real physical devices; therefore
the added overhead is not really justified.

Many network cards use counters in hardware to count packets/bytes
and there is no expectation of atomic access there.
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