From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mathieu Desnoyers Subject: Re: [PATCH] netfilter: use per-CPU recursive lock {XV} Date: Sun, 26 Apr 2009 15:31:35 -0400 Message-ID: <20090426193135.GA30851@Krystal> References: <20090421111541.228e977a@nehalam> <20090421193924.GA24404@elte.hu> <20090421143927.52d7d89d@nehalam> <20090423210938.1501507b@nehalam> <49F146FF.5050200@cosmosbay.com> <20090424091839.6e13ebec@nehalam> <49F22465.80305@gmail.com> <20090425133052.4cb711f5@nehalam> <49F4A6E3.7080102@cosmosbay.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: Stephen Hemminger , David Miller , Jarek Poplawski , Linus Torvalds , Ingo Molnar , Paul Mackerras , paulmck@linux.vnet.ibm.com, Evgeniy Polyakov , kaber@trash.net, jeff.chua.linux@gmail.com, laijs@cn.fujitsu.com, jengelh@medozas.de, r000n@r000n.net, linux-kernel@vger.kernel.org, netfilter-devel@vger.kernel.org, netdev@vger.kernel.org, benh@kernel.crashing.org To: Eric Dumazet Return-path: Content-Disposition: inline In-Reply-To: <49F4A6E3.7080102@cosmosbay.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netfilter-devel.vger.kernel.org * Eric Dumazet (dada1@cosmosbay.com) wrote: > From: Stephen Hemminger > > > Epilogue due to master Jarek. Lockdep carest not about the locking > > doth bestowed. Therefore no keys are needed. > > > > Signed-off-by: Stephen Hemminger > > So far, so good, should be ready for inclusion now, nobody complained :) > > I include the final patch, merge of your last two patches. > > David, could you please review it once again and apply it if it's OK ? > [...] > +/* > + * Per-CPU read/write lock associated with per-cpu table entries. > + * This is not a general solution but makes reader locking fast since > + * there is no shared variable to cause cache ping-pong; but adds an > + * additional write-side penalty since update must lock all > + * possible CPU's. > + * > + * Read lock is used by ip/arp/ip6 tables rule processing which runs per-cpu. > + * It needs to ensure that the rules are not being changed while packet > + * is being processed. In some cases, the read lock will be acquired > + * twice on the same CPU; this is okay because read locks handle nesting. > + * > + * Write lock is used in two cases: > + * 1. reading counter values > + * all readers need to be stopped and the per-CPU values are summed. > + * > + * 2. replacing tables > + * any readers that are using the old tables have to complete > + * before freeing the old table. This is handled by reading > + * as a side effect of reading counters > + */ > +DECLARE_PER_CPU(rwlock_t, xt_info_locks); > + > +static inline void xt_info_rdlock_bh(void) > +{ > + /* > + * Note: can not use read_lock_bh(&__get_cpu_var(xt_info_locks)) > + * because need to ensure that preemption is disable before > + * acquiring per-cpu-variable, so do it as a two step process > + */ > + local_bh_disable(); Why do you need to disable bottom halves on the read-side ? You could probably just disable preemption, given this lock is nestable on the read-side anyway. Or I'm missing something obvious ? > + read_lock(&__get_cpu_var(xt_info_locks)); > +} > + > +static inline void xt_info_rdunlock_bh(void) > +{ > + read_unlock_bh(&__get_cpu_var(xt_info_locks)); > +} > + > +static inline void xt_info_wrlock(unsigned int cpu) > +{ > + write_lock(&per_cpu(xt_info_locks, cpu)); > +} > + > +static inline void xt_info_wrunlock(unsigned int cpu) > +{ > + > + write_unlock(&per_cpu(xt_info_locks, cpu)); > +} > [...] Mathieu -- Mathieu Desnoyers OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68