From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH] virtio-net: fix a race on 32bit arches Date: Wed, 6 Jun 2012 22:58:15 +0300 Message-ID: <20120606195814.GA20677@redhat.com> References: <1338971724.2760.3913.camel@edumazet-glaptop> <1338972341.2760.3944.camel@edumazet-glaptop> <20120606111357.GA15070@redhat.com> <1338988210.2760.4485.camel@edumazet-glaptop> <20120606144941.GA17092@redhat.com> <20120606081432.6b602065@nehalam.linuxnetplumber.net> <20120606185107.GA20503@redhat.com> <1339012441.26966.48.camel@edumazet-glaptop> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Stephen Hemminger To: Eric Dumazet Return-path: Content-Disposition: inline In-Reply-To: <1339012441.26966.48.camel@edumazet-glaptop> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org List-Id: netdev.vger.kernel.org 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: > > > 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. -- MST