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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