From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756292Ab0LQUzV (ORCPT ); Fri, 17 Dec 2010 15:55:21 -0500 Received: from e5.ny.us.ibm.com ([32.97.182.145]:33703 "EHLO e5.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756201Ab0LQUzJ (ORCPT ); Fri, 17 Dec 2010 15:55:09 -0500 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, eric.dumazet@gmail.com, darren@dvhart.com, "Paul E. McKenney" Subject: [PATCH RFC tip/core/rcu 18/20] rcu: reduce __call_rcu()-induced contention on rcu_node structures Date: Fri, 17 Dec 2010 12:54:49 -0800 Message-Id: <1292619291-2468-18-git-send-email-paulmck@linux.vnet.ibm.com> X-Mailer: git-send-email 1.7.3.2 In-Reply-To: <20101217205433.GA10199@linux.vnet.ibm.com> References: <20101217205433.GA10199@linux.vnet.ibm.com> X-Content-Scanned: Fidelis XPS MAILER Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When the current __call_rcu() function was written, the expedited APIs did not exist. The __call_rcu() implementation therefore went to great lengths to detect the end of old grace periods and to start new ones, all in the name of reducing grace-period latency. Now the expedited APIs do exist, and the usage of __call_rcu() has increased considerably. This commit therefore causes __call_rcu() to avoid worrying about grace periods unless there are a large number of RCU callbacks stacked up on the current CPU. Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 38 +++++++++++++++++++++----------------- 1 files changed, 21 insertions(+), 17 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 01c8ad3..d0ddfea 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1435,22 +1435,11 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), */ local_irq_save(flags); rdp = this_cpu_ptr(rsp->rda); - rcu_process_gp_end(rsp, rdp); - check_for_new_grace_period(rsp, rdp); /* Add the callback to our list. */ *rdp->nxttail[RCU_NEXT_TAIL] = head; rdp->nxttail[RCU_NEXT_TAIL] = &head->next; - /* Start a new grace period if one not already started. */ - if (!rcu_gp_in_progress(rsp)) { - unsigned long nestflag; - struct rcu_node *rnp_root = rcu_get_root(rsp); - - raw_spin_lock_irqsave(&rnp_root->lock, nestflag); - rcu_start_gp(rsp, nestflag); /* releases rnp_root->lock. */ - } - /* * Force the grace period if too many callbacks or too long waiting. * Enforce hysteresis, and don't invoke force_quiescent_state() @@ -1459,12 +1448,27 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), * is the only one waiting for a grace period to complete. */ if (unlikely(++rdp->qlen > rdp->qlen_last_fqs_check + qhimark)) { - rdp->blimit = LONG_MAX; - if (rsp->n_force_qs == rdp->n_force_qs_snap && - *rdp->nxttail[RCU_DONE_TAIL] != head) - force_quiescent_state(rsp, 0); - rdp->n_force_qs_snap = rsp->n_force_qs; - rdp->qlen_last_fqs_check = rdp->qlen; + + /* Are we ignoring a completed grace period? */ + rcu_process_gp_end(rsp, rdp); + check_for_new_grace_period(rsp, rdp); + + /* Start a new grace period if one not already started. */ + if (!rcu_gp_in_progress(rsp)) { + unsigned long nestflag; + struct rcu_node *rnp_root = rcu_get_root(rsp); + + raw_spin_lock_irqsave(&rnp_root->lock, nestflag); + rcu_start_gp(rsp, nestflag); /* rlses rnp_root->lock */ + } else { + /* Give the grace period a kick. */ + rdp->blimit = LONG_MAX; + if (rsp->n_force_qs == rdp->n_force_qs_snap && + *rdp->nxttail[RCU_DONE_TAIL] != head) + force_quiescent_state(rsp, 0); + rdp->n_force_qs_snap = rsp->n_force_qs; + rdp->qlen_last_fqs_check = rdp->qlen; + } } else if (ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs), jiffies)) force_quiescent_state(rsp, 1); local_irq_restore(flags); -- 1.7.3.2