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Date: Sun, 6 Dec 2009 19:22:10 +0100 From: Jarek Poplawski <jarkao2@...il.com> To: Eric Dumazet <eric.dumazet@...il.com> Cc: "David S. Miller" <davem@...emloft.net>, Linux Netdev List <netdev@...r.kernel.org> Subject: Re: [PATCH] inetpeer: optimizations On Sun, Dec 06, 2009 at 09:47:03AM +0100, Eric Dumazet wrote: > Jarek Poplawski a écrit : > > Eric Dumazet wrote, On 12/05/2009 01:11 PM: > > > >> - Use atomic_dec_and_test() in inet_putpeer() > > > > atomic_dec_and_lock()? > > Yes :) > > > > >> This takes/dirties the lock only if necessary. > > ... > > > >> void inet_putpeer(struct inet_peer *p) > >> { > >> - spin_lock_bh(&inet_peer_unused_lock); > >> - if (atomic_dec_and_test(&p->refcnt)) { > >> - list_add_tail(&p->unused, &unused_peers); > >> + local_bh_disable(); > >> + if (atomic_dec_and_lock(&p->refcnt, &unused_peers.lock)) { > > > > Why not: > > if (atomic_dec_and_test(&p->refcnt)) { > > spin_lock_bh(&inet_peer_unused_lock); > > ... > > Because we have to take the lock before doing the final 1 -> 0 refcount transition. > > (Another thread could do the 0 -> 1 transition) AFAICS this lock here can only to prevent double linking to the unused_peers list during such transitions. If so, it could be replaced with the list_empty(&p->unused) test before list_add_tail(), and atomic_dec_test() without the lock would be enough (unless I miss something ;-). Jarek P. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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