netdev - Re: [PATCH net-next-2.6] tg3: 64bits stats

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Date:	Mon, 05 Jul 2010 20:07:10 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ben Hutchings <bhutchings@...arflare.com>
Cc:	Matt Carlson <mcarlson@...adcom.com>,
	Michael Chan <mchan@...adcom.com>,
	netdev <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>
Subject: Re: [PATCH net-next-2.6] tg3: 64bits stats

Le lundi 05 juillet 2010 à 18:31 +0100, Ben Hutchings a écrit :
> On Mon, 2010-07-05 at 18:03 +0200, Eric Dumazet wrote:
> > Le lundi 05 juillet 2010 à 11:14 +0200, Eric Dumazet a écrit :
> > > After commit be1f3c2c027c (net: Enable 64-bit net device statistics on
> > > 32-bit architectures), we can now provide 64bit stats, even on 32bit
> > > arches.
> > > 
> > > Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
> > > ---
> > 
> > Please disregard this patch.
> > 
> > There is small possibility a reader might read a 64bit value while
> > another writer makes a change to it, changing high 32bit value.
> > 
> > A change in core network would be needed to make this 100% safe,
> > possibly using a seqlock to protect dev->stats64
> 
> I really didn't want to add this overhead and complication to readers
> when only some drivers need it.
> 

Overhead would be minimal, only in get_stats() method and only for
drivers that want to provide 64 bit stats...

Clearly, rx/tx path must not have any overhead.

Right now, even RTNL 64bit stats are not safe.

Should we revert prior patches or try to make progress ?



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