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

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Message-ID: <20120606204335.GA23552@redhat.com>
Date:	Wed, 6 Jun 2012 23:43:35 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Ben Hutchings <bhutchings@...arflare.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Stephen Hemminger <shemminger@...tta.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, Jun 06, 2012 at 09:35:04PM +0100, Ben Hutchings wrote:
> On Wed, 2012-06-06 at 23:16 +0300, Michael S. Tsirkin wrote:
> > On Wed, Jun 06, 2012 at 10:08:09PM +0200, Eric Dumazet wrote:
> > > On Wed, 2012-06-06 at 22:58 +0300, Michael S. Tsirkin wrote:
> > > 
> > > > 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.
> > > 
> > > Which lock do you own in the RX path ?
> > 
> > We can just disable napi, everything is updated from napi callback.
> 
> Seriously, though: don't do that; this is going to hurt performance for
> minimal benefit.
> 
> Ben.

Yea, it doesn't work anyway. Maybe take a xmit lock for tx and keep
using the per-cpu counters for rx. Or does this sound too disruptive
too?

> > > You'll have to add a lock in fast path. This sounds really a bad choice
> > > to me.
> > 
> > .ndo_get_stats64 is not data path though, is it?
> > 
> 
> -- 
> Ben Hutchings, Staff Engineer, Solarflare
> Not speaking for my employer; that's the marketing department's job.
> They asked us to note that Solarflare product names are trademarked.
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