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Message-ID: <4BAECDA0.6050300@cn.fujitsu.com>
Date: Sun, 28 Mar 2010 11:31:44 +0800
From: Lai Jiangshan <laijs@...fujitsu.com>
To: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Ingo Molnar <mingo@...e.hu>,
LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] rcu: check dynticks idle cpu when start gp
Currently, if there are/is dynticks idle CPU(s), GPs
can not end until we force_quiescent_state().
It means we delay our GP frequently.
It also means we do non-fastpath work(force QS) frequently.
This patch add a _hint_ mask to struct rcu_node, and
check dynticks idle cpu when start gp.
Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
---
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 1947c4e..a85c5c4 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -666,6 +666,62 @@ rcu_start_gp_per_cpu(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_dat
__note_new_gpnum(rsp, rnp, rdp);
}
+static void rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp,
+ struct rcu_node *rnp, unsigned long flags);
+
+static inline void rcu_check_recent_offcpus(struct rcu_state *rsp,
+ struct rcu_node *rnp, unsigned long flags)
+ __releases(rnp->lock)
+{
+#ifdef CONFIG_SMP
+#if defined(CONFIG_NO_HZ) || defined(CONFIG_HOTPLUG_CPU)
+ /*
+ * if it is leaf node and there are some CPU being dynticks state
+ * or offline-ing recently, we will check and report qs
+ * for these CPU when needed.
+ * (for nonleaf node, rnp->offmask is always 0)
+ */
+ if (rnp->qsmask & rnp->offmask) {
+ int cpu;
+ unsigned long bit;
+ unsigned long mask = rnp->qsmask & rnp->offmask;
+ struct rcu_data *rdp;
+ long curr, curr_nmi;
+ int off;
+
+ cpu = rnp->grplo;
+ bit = 1;
+ for (; cpu <= rnp->grphi; cpu++, bit <<= 1) {
+ if (!(mask & bit))
+ continue;
+
+ rdp = rsp->rda[cpu];
+ curr = rdp->dynticks->dynticks;
+ curr_nmi = rdp->dynticks->dynticks_nmi;
+
+ off = ((curr & 0x1) == 0) && ((curr_nmi & 0x1) == 0);
+ off = off || cpu_is_offline(rdp->cpu);
+
+ if (!off)
+ mask &= ~bit;
+ }
+
+ rnp->offmask = mask;
+ if (mask) {
+ /*
+ * It is impossible that rcu_report_qs_rnp()
+ * calls rcu_report_qs_rsp() again. So we
+ * will not cause recursion.
+ */
+ rcu_report_qs_rnp(mask, rsp, rnp, flags);
+ return;
+ }
+ }
+#endif
+#endif
+ raw_spin_unlock_irqrestore(&rnp->lock, flags);
+}
+
/*
* Start a new RCU grace period if warranted, re-initializing the hierarchy
* in preparation for detecting the next grace period. The caller must hold
@@ -717,7 +773,7 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
rnp->completed = rsp->completed;
rsp->signaled = RCU_SIGNAL_INIT; /* force_quiescent_state OK. */
rcu_start_gp_per_cpu(rsp, rnp, rdp);
- raw_spin_unlock_irqrestore(&rnp->lock, flags);
+ rcu_check_recent_offcpus(rsp, rnp, flags);
return;
}
@@ -745,14 +801,20 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
* irqs disabled.
*/
rcu_for_each_node_breadth_first(rsp, rnp) {
- raw_spin_lock(&rnp->lock); /* irqs already disabled. */
+ unsigned long tmp_flags;
+
+ /* irqs already disabled */
+ raw_spin_lock_irqsave(&rnp->lock, tmp_flags);
+
rcu_preempt_check_blocked_tasks(rnp);
rnp->qsmask = rnp->qsmaskinit;
rnp->gpnum = rsp->gpnum;
rnp->completed = rsp->completed;
if (rnp == rdp->mynode)
rcu_start_gp_per_cpu(rsp, rnp, rdp);
- raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
+
+ rcu_check_recent_offcpus(rsp, rnp, tmp_flags);
+ /* irqs remain disabled. */
}
rnp = rcu_get_root(rsp);
@@ -1190,8 +1252,10 @@ static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *))
cpu = rnp->grplo;
bit = 1;
for (; cpu <= rnp->grphi; cpu++, bit <<= 1) {
- if ((rnp->qsmask & bit) != 0 && f(rsp->rda[cpu]))
+ if ((rnp->qsmask & bit) != 0 && f(rsp->rda[cpu])) {
mask |= bit;
+ rnp->offmask |= bit;
+ }
}
if (mask != 0) {
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index 4a525a3..8ec96a7 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -104,6 +104,8 @@ struct rcu_node {
/* an rcu_data structure, otherwise, each */
/* bit corresponds to a child rcu_node */
/* structure. */
+ unsigned long offmask; /* Track CPUs which are dynticks state */
+ /* or offline-ing recently. */
unsigned long expmask; /* Groups that have ->blocked_tasks[] */
/* elements that need to drain to allow the */
/* current expedited grace period to */
--
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