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

On Wed, Jun 06, 2012 at 09:54:01PM +0200, Eric Dumazet wrote:

On Wed, 2012-06-06 at 21:51 +0300, Michael S. Tsirkin wrote:

quoted

BTW for cards that do implement the counters in software,
under xmit lock, is anything wrong with simply taking the xmit lock
when we get the stats instead of the per-cpu trick + seqlock?

I still dont understand why you would do that.

Most modern machines are 64bits, so there is no seqlock overhead,
nothing at all.

If you focus on 32bit hardware, just stick on 32bit counters ?

These wrap around.

Note that most u64_stats_sync users are virtual drivers, without xmit
lock (LLTX drivers)

Absolutely, I am talking about virtio here.  I'm not kicking
u64_stats_sync idea I am just saying that simple locking
would work for virtio and might be better as it
gives us a way to get counters atomically.


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MST