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Date: Wed, 06 Jun 2012 22:06:11 +0200 From: Eric Dumazet <eric.dumazet@...il.com> To: "Michael S. Tsirkin" <mst@...hat.com> Cc: Jason Wang <jasowang@...hat.com>, netdev@...r.kernel.org, rusty@...tcorp.com.au, linux-kernel@...r.kernel.org, virtualization@...ts.linux-foundation.org, Stephen Hemminger <shemminger@...tta.com> Subject: Re: [PATCH] virtio-net: fix a race on 32bit arches On Wed, 2012-06-06 at 21:43 +0300, Michael S. Tsirkin wrote: > 1. We are trying to look at counters for purposes of tuning the device. > E.g. if ethtool reports packets and bytes, we'd like to calculate > average packet size by bytes/packets. > > If both counters are read atomically the metric becomes more exact. > Not a must but nice to have. > metrics are exact right now. As soon as you read a value, it might already have changed. Maybe you want to stop_machine() to make sure all the metrics you want are 'exact' ;) > 2. 32 bit systems have some overhead because of the seqlock. > virtio could instead simply keep tx counters in the queue structure, and > get the tx lock when they are read. > But then you need atomic64 stuff, have you an idea of the cost of such primitives on 32bit ? 3. use 32bit counters on 32bit arches, as many drivers still do ? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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