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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, fweisbec@gmail.com, sbw@mit.edu, patches@linaro.org, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 20/22] rcu: Move RCU grace-period cleanup into kthread Date: Fri, 22 Jun 2012 08:17:19 -0700 Message-Id: <1340378241-6458-20-git-send-email-paulmck@linux.vnet.ibm.com> X-Mailer: git-send-email 1.7.8 In-Reply-To: <1340378241-6458-1-git-send-email-paulmck@linux.vnet.ibm.com> References: <20120622151655.GA6249@linux.vnet.ibm.com> <1340378241-6458-1-git-send-email-paulmck@linux.vnet.ibm.com> X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12062215-7182-0000-0000-000001D2B5F4 X-Gm-Message-State: ALoCoQkHnwJFShXCJGasHLvBLuymnVnLhTEXRXtOu3aXKbu9rHmx3sL8S0P3od28GSe9fV+jgoEQ From: "Paul E. McKenney" As a first step towards allowing grace-period cleanup to be preemptible, this commit moves the RCU grace-period cleanup into the same kthread that is now used to initialize grace periods. This is needed to keep scheduling latency down to a dull roar. Reported-by: Mike Galbraith Reported-by: Dimitri Sivanich Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 112 ++++++++++++++++++++++++++++++------------------------ 1 files changed, 62 insertions(+), 50 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index e5b4532..4a3f6b0 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1035,6 +1035,7 @@ rcu_start_gp_per_cpu(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_dat static int rcu_gp_kthread(void *arg) { unsigned long flags; + unsigned long gp_duration; struct rcu_data *rdp; struct rcu_node *rnp; struct rcu_state *rsp = arg; @@ -1125,6 +1126,65 @@ static int rcu_gp_kthread(void *arg) rsp->fqs_state = RCU_SIGNAL_INIT; raw_spin_unlock_irqrestore(&rnp->lock, flags); put_online_cpus(); + + /* Handle grace-period end. */ + rnp = rcu_get_root(rsp); + for (;;) { + wait_event_interruptible(rsp->gp_wq, + !ACCESS_ONCE(rnp->qsmask) && + !rcu_preempt_blocked_readers_cgp(rnp)); + if (!ACCESS_ONCE(rnp->qsmask) && + !rcu_preempt_blocked_readers_cgp(rnp)) + break; + flush_signals(current); + } + + raw_spin_lock_irqsave(&rnp->lock, flags); + gp_duration = jiffies - rsp->gp_start; + if (gp_duration > rsp->gp_max) + rsp->gp_max = gp_duration; + + /* + * We know the grace period is complete, but to everyone else + * it appears to still be ongoing. But it is also the case + * that to everyone else it looks like there is nothing that + * they can do to advance the grace period. It is therefore + * safe for us to drop the lock in order to mark the grace + * period as completed in all of the rcu_node structures. + * + * But if this CPU needs another grace period, it will take + * care of this while initializing the next grace period. + * We use RCU_WAIT_TAIL instead of the usual RCU_DONE_TAIL + * because the callbacks have not yet been advanced: Those + * callbacks are waiting on the grace period that just now + * completed. + */ + if (*rdp->nxttail[RCU_WAIT_TAIL] == NULL) { + raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ + + /* + * Propagate new ->completed value to rcu_node + * structures so that other CPUs don't have to + * wait until the start of the next grace period + * to process their callbacks. + */ + rcu_for_each_node_breadth_first(rsp, rnp) { + /* irqs already disabled. */ + raw_spin_lock(&rnp->lock); + rnp->completed = rsp->gpnum; + /* irqs remain disabled. */ + raw_spin_unlock(&rnp->lock); + } + rnp = rcu_get_root(rsp); + raw_spin_lock(&rnp->lock); /* irqs already disabled. */ + } + + rsp->completed = rsp->gpnum; /* Declare grace period done. */ + trace_rcu_grace_period(rsp->name, rsp->completed, "end"); + rsp->fqs_state = RCU_GP_IDLE; + if (cpu_needs_another_gp(rsp, rdp)) + rsp->gp_flags = 1; + raw_spin_unlock_irqrestore(&rnp->lock, flags); } return 0; } @@ -1172,57 +1232,9 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags) static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags) __releases(rcu_get_root(rsp)->lock) { - unsigned long gp_duration; - struct rcu_node *rnp = rcu_get_root(rsp); - struct rcu_data *rdp = this_cpu_ptr(rsp->rda); - WARN_ON_ONCE(!rcu_gp_in_progress(rsp)); - - /* - * Ensure that all grace-period and pre-grace-period activity - * is seen before the assignment to rsp->completed. - */ - smp_mb(); /* See above block comment. */ - gp_duration = jiffies - rsp->gp_start; - if (gp_duration > rsp->gp_max) - rsp->gp_max = gp_duration; - - /* - * We know the grace period is complete, but to everyone else - * it appears to still be ongoing. But it is also the case - * that to everyone else it looks like there is nothing that - * they can do to advance the grace period. It is therefore - * safe for us to drop the lock in order to mark the grace - * period as completed in all of the rcu_node structures. - * - * But if this CPU needs another grace period, it will take - * care of this while initializing the next grace period. - * We use RCU_WAIT_TAIL instead of the usual RCU_DONE_TAIL - * because the callbacks have not yet been advanced: Those - * callbacks are waiting on the grace period that just now - * completed. - */ - if (*rdp->nxttail[RCU_WAIT_TAIL] == NULL) { - raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ - - /* - * Propagate new ->completed value to rcu_node structures - * so that other CPUs don't have to wait until the start - * of the next grace period to process their callbacks. - */ - rcu_for_each_node_breadth_first(rsp, rnp) { - raw_spin_lock(&rnp->lock); /* irqs already disabled. */ - rnp->completed = rsp->gpnum; - raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ - } - rnp = rcu_get_root(rsp); - raw_spin_lock(&rnp->lock); /* irqs already disabled. */ - } - - rsp->completed = rsp->gpnum; /* Declare the grace period complete. */ - trace_rcu_grace_period(rsp->name, rsp->completed, "end"); - rsp->fqs_state = RCU_GP_IDLE; - rcu_start_gp(rsp, flags); /* releases root node's rnp->lock. */ + raw_spin_unlock_irqrestore(&rcu_get_root(rsp)->lock, flags); + wake_up(&rsp->gp_wq); /* Memory barrier implied by wake_up() path. */ } /*