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

From: Stephen Hemminger <[email-masked]>
Date: Wed, 6 Jun 2012 08:14:32 -0700

On Wed, 6 Jun 2012 17:49:42 +0300
"Michael S. Tsirkin" <[email-masked]> 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.