netdev - Re: [Bridge] [PATCH] bridge: per-cpu packet statistics

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Date:	Tue, 2 Mar 2010 09:22:09 -0800
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	netdev@...r.kernel.org, bridge@...ts.linux-foundation.org,
	David Miller <davem@...emloft.net>
Subject: Re: [Bridge] [PATCH]  bridge: per-cpu packet statistics

On Tue, 02 Mar 2010 07:01:30 +0100
Eric Dumazet <eric.dumazet@...il.com> wrote:

> Le lundi 01 mars 2010 à 16:16 -0800, Stephen Hemminger a écrit :
> > The shared packet statistics are a potential source of slow down
> > on bridged traffic. Convert to per-cpu array, but only keep those
> > statistics which change per-packet.
> > 
> > Signed-off-by: Stephen Hemminger <shemminger@...tta.com>
> > 
> > ---
> > 
> >  net/bridge/br_device.c  |   43 ++++++++++++++++++++++++++++++++++++++-----
> >  net/bridge/br_if.c      |    6 ++++++
> >  net/bridge/br_input.c   |    5 +++--
> >  net/bridge/br_private.h |    8 ++++++++
> >  4 files changed, 55 insertions(+), 7 deletions(-)
> > 
> > --- a/net/bridge/br_device.c	2010-03-01 08:22:23.476657998 -0800
> > +++ b/net/bridge/br_device.c	2010-03-01 15:31:36.737227465 -0800
> > @@ -26,11 +26,12 @@ netdev_tx_t br_dev_xmit(struct sk_buff *
> >  	const unsigned char *dest = skb->data;
> >  	struct net_bridge_fdb_entry *dst;
> >  	struct net_bridge_mdb_entry *mdst;
> > +	struct br_cpu_netstats *brstats = this_cpu_ptr(br->stats);
> >  
> > -	BR_INPUT_SKB_CB(skb)->brdev = dev;
> > +	brstats->tx_packets++;
> > +	brstats->tx_bytes += skb->len;
> 
> 
> On TX path, this is not really necessary, since we already dirtied
> txq->lock before calling br_dev_xmit(), we can use txq->tx_packets and
> txq->tx_bytes for free ?

Bridge is already using lockless transmit LLTX, so tx_lock is not touched.
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