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

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Date:	Tue, 3 Jan 2012 12:01:27 -0000
From:	"David Laight" <David.Laight@...LAB.COM>
To:	<pablo@...filter.org>, <netfilter-devel@...r.kernel.org>
Cc:	<davem@...emloft.net>, <netdev@...r.kernel.org>
Subject: RE: [PATCH 06/19] netfilter: nf_conntrack: use atomic64 for accounting counters

 
>  		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.

	David


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