netdev - Re: [net-next PATCH] igb: update adapter stats when reading /proc/net/dev.

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Date:	Tue, 05 Oct 2010 16:53:13 +0200
From:	Jesper Dangaard Brouer <hawk@...x.dk>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	Jeff Kirsher <jeffrey.t.kirsher@...el.com>
Subject: Re: [net-next PATCH] igb: update adapter stats when reading
 /proc/net/dev.

On Tue, 2010-10-05 at 16:41 +0200, Eric Dumazet wrote:
> Le mardi 05 octobre 2010 à 16:18 +0200, Jesper Dangaard Brouer a écrit :
> > Network driver igb: Improve the accuracy of stats in /proc/net/dev, by
> > updating the adapter stats when reading /proc/net/dev.  Currently the
> > stats are updated by the watchdog timer every 2 sec, or when getting
> > stats via ethtool -S.
> > 
> > A number of userspace apps read these /proc/net/dev stats every second,
> > e.g. ifstat, which then gives a perceived very bursty traffic pattern,
> > which is actually false.
> > 
> > Signed-off-by: Jesper Dangaard Brouer <hawk@...x.dk>
> 
> Unfortunately this is racy with igb_watchdog_task()
> 
> igb_update_stats() must be called under protection of a lock.

Its already racy, because "ethtool -S" reads out the stats immediately,
and thus races with the timer.

See: igb_ethtool.c
 igb_get_ethtool_stats() invoke igb_update_stats(adapter);

-- 
Med venlig hilsen / Best regards
  Jesper Brouer
  ComX Networks A/S
  Linux Network Kernel Developer
  Cand. Scient Datalog / MSc.CS
  Author of http://adsl-optimizer.dk
  LinkedIn: http://www.linkedin.com/in/brouer


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