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Date: Mon, 7 Jul 2014 15:38:15 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: linux-kernel@...r.kernel.org
Cc: mingo@...nel.org, laijs@...fujitsu.com, dipankar@...ibm.com,
akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
josh@...htriplett.org, niv@...ibm.com, tglx@...utronix.de,
peterz@...radead.org, rostedt@...dmis.org, dhowells@...hat.com,
edumazet@...gle.com, dvhart@...ux.intel.com, fweisbec@...il.com,
oleg@...hat.com, sbw@....edu,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 11/17] rcu: Bind grace-period kthreads to non-NO_HZ_FULL CPUs
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Binding the grace-period kthreads to the timekeeping CPU resulted in
significant performance decreases for some workloads. For more detail,
see:
https://lkml.org/lkml/2014/6/3/395 for benchmark numbers
https://lkml.org/lkml/2014/6/4/218 for CPU statistics
It turns out that it is necessary to bind the grace-period kthreads
to the timekeeping CPU only when all but CPU 0 is a nohz_full CPU
on the one hand or if CONFIG_NO_HZ_FULL_SYSIDLE=y on the other.
In other cases, it suffices to bind the grace-period kthreads to the
set of non-nohz_full CPUs.
This commit therefore creates a tick_nohz_not_full_mask that is the
complement of tick_nohz_full_mask, and then binds the grace-period
kthread to the set of CPUs indicated by this new mask, which covers
the CONFIG_NO_HZ_FULL_SYSIDLE=n case. The CONFIG_NO_HZ_FULL_SYSIDLE=y
case still binds the grace-period kthreads to the timekeeping CPU.
This commit also includes the tick_nohz_full_enabled() check suggested
by Frederic Weisbecker.
Reported-by: Jet Chen <jet.chen@...el.com>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
[ paulmck: Created housekeeping_affine() per fweisbec feedback. ]
---
include/linux/tick.h | 19 +++++++++++++++++++
kernel/rcu/tree_plugin.h | 14 +++++++++-----
kernel/time/tick-sched.c | 10 ++++++++++
3 files changed, 38 insertions(+), 5 deletions(-)
diff --git a/include/linux/tick.h b/include/linux/tick.h
index b84773cb9f4c..c39af3261351 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -12,6 +12,7 @@
#include <linux/hrtimer.h>
#include <linux/context_tracking_state.h>
#include <linux/cpumask.h>
+#include <linux/sched.h>
#ifdef CONFIG_GENERIC_CLOCKEVENTS
@@ -162,6 +163,7 @@ static inline u64 get_cpu_iowait_time_us(int cpu, u64 *unused) { return -1; }
#ifdef CONFIG_NO_HZ_FULL
extern bool tick_nohz_full_running;
extern cpumask_var_t tick_nohz_full_mask;
+extern cpumask_var_t tick_nohz_not_full_mask;
static inline bool tick_nohz_full_enabled(void)
{
@@ -194,6 +196,23 @@ static inline void tick_nohz_full_kick_all(void) { }
static inline void __tick_nohz_task_switch(struct task_struct *tsk) { }
#endif
+static inline bool is_housekeeping_cpu(int cpu)
+{
+#ifdef CONFIG_NO_HZ_FULL
+ if (tick_nohz_full_enabled())
+ return cpumask_test_cpu(cpu, tick_nohz_not_full_mask);
+#endif
+ return true;
+}
+
+static inline void housekeeping_affine(struct task_struct *t)
+{
+#ifdef CONFIG_NO_HZ_FULL
+ if (tick_nohz_full_enabled())
+ set_cpus_allowed_ptr(t, tick_nohz_not_full_mask);
+#endif
+}
+
static inline void tick_nohz_full_check(void)
{
if (tick_nohz_full_enabled())
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 719587af7b10..b39ba7239bd6 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2846,12 +2846,16 @@ static bool rcu_nohz_full_cpu(struct rcu_state *rsp)
*/
static void rcu_bind_gp_kthread(void)
{
-#ifdef CONFIG_NO_HZ_FULL
- int cpu = tick_do_timer_cpu;
+ int __maybe_unused cpu;
- if (cpu < 0 || cpu >= nr_cpu_ids)
+ if (!tick_nohz_full_enabled())
return;
- if (raw_smp_processor_id() != cpu)
+#ifdef CONFIG_NO_HZ_FULL_SYSIDLE
+ cpu = tick_do_timer_cpu;
+ if (cpu >= 0 && cpu < nr_cpu_ids && raw_smp_processor_id() != cpu)
set_cpus_allowed_ptr(current, cpumask_of(cpu));
-#endif /* #ifdef CONFIG_NO_HZ_FULL */
+#else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
+ if (!is_housekeeping_cpu(raw_smp_processor_id()))
+ housekeeping_affine(current);
+#endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
}
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 6558b7ac112d..e023134d63a1 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -154,6 +154,7 @@ static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs)
#ifdef CONFIG_NO_HZ_FULL
cpumask_var_t tick_nohz_full_mask;
+cpumask_var_t tick_nohz_not_full_mask;
bool tick_nohz_full_running;
static bool can_stop_full_tick(void)
@@ -281,6 +282,7 @@ static int __init tick_nohz_full_setup(char *str)
int cpu;
alloc_bootmem_cpumask_var(&tick_nohz_full_mask);
+ alloc_bootmem_cpumask_var(&tick_nohz_not_full_mask);
if (cpulist_parse(str, tick_nohz_full_mask) < 0) {
pr_warning("NOHZ: Incorrect nohz_full cpumask\n");
return 1;
@@ -291,6 +293,8 @@ static int __init tick_nohz_full_setup(char *str)
pr_warning("NO_HZ: Clearing %d from nohz_full range for timekeeping\n", cpu);
cpumask_clear_cpu(cpu, tick_nohz_full_mask);
}
+ cpumask_andnot(tick_nohz_not_full_mask,
+ cpu_possible_mask, tick_nohz_full_mask);
tick_nohz_full_running = true;
return 1;
@@ -332,9 +336,15 @@ static int tick_nohz_init_all(void)
pr_err("NO_HZ: Can't allocate full dynticks cpumask\n");
return err;
}
+ if (!alloc_cpumask_var(&tick_nohz_not_full_mask, GFP_KERNEL)) {
+ pr_err("NO_HZ: Can't allocate not-full dynticks cpumask\n");
+ return err;
+ }
err = 0;
cpumask_setall(tick_nohz_full_mask);
cpumask_clear_cpu(smp_processor_id(), tick_nohz_full_mask);
+ cpumask_clear(tick_nohz_not_full_mask);
+ cpumask_set_cpu(smp_processor_id(), tick_nohz_not_full_mask);
tick_nohz_full_running = true;
#endif
return err;
--
1.8.1.5
--
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