netdev - RE: [PATCH 06/19] netfilter: nf_conntrack: use atomic64 for accounting counters

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Message-ID: <1325597877.2320.47.camel@edumazet-HP-Compaq-6005-Pro-SFF-PC>
Date:	Tue, 03 Jan 2012 14:37:57 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Laight <David.Laight@...LAB.COM>
Cc:	pablo@...filter.org, netfilter-devel@...r.kernel.org,
	davem@...emloft.net, netdev@...r.kernel.org
Subject: RE: [PATCH 06/19] netfilter: nf_conntrack: use atomic64 for
 accounting counters

Le mardi 03 janvier 2012 à 14:31 +0100, Eric Dumazet a écrit :
> Le mardi 03 janvier 2012 à 12:01 +0000, David Laight a écrit :
> > >  		if (acct) {
> > > -			spin_lock_bh(&ct->lock);
> > > -			acct[CTINFO2DIR(ctinfo)].packets++;
> > > -			acct[CTINFO2DIR(ctinfo)].bytes += skb->len;
> > > -			spin_unlock_bh(&ct->lock);
> > > +			atomic64_inc(&acct[CTINFO2DIR(ctinfo)].packets);
> > > +			atomic64_add(skb->len,
> > &acct[CTINFO2DIR(ctinfo)].bytes);
> > >  		}
> > 
> > On a 32bit arch the two atomic64 operations require a locked
> > bus cycle each. The spin_unlock_bh() may not need one - so
> > the code may now be slower (modulo lock contention etc).
> > 
> > Probably worth caching &acct[CTINFO2DIR(ctinfo)] in a local,
> > the compiler probably can't do it itself.
> 
> You're mistaken.
> 
> Compile a UP kernel and check yourself before doing such claims.
> 
> 

Oops sorry, I misread your mail, I thought you were speaking of UP
kernel.



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