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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2014-06-04 13:46:03 -0700
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2014-07-09 09:15:02 -0700
commitc0f489d2c6fec8994c642c2ec925eb858727dc7b (patch)
treee72f709231a498626a149ef676bd60ff0e1b26c3 /kernel/rcu
parentabaa93d9e1de2c29297e69ddba8ddd38f15064cf (diff)
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rcu: Bind grace-period kthreads to non-NO_HZ_FULL CPUs
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@intel.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> [ paulmck: Created housekeeping_affine() and housekeeping_mask per fweisbec feedback. ]
Diffstat (limited to 'kernel/rcu')
-rw-r--r--kernel/rcu/tree_plugin.h14
1 files changed, 9 insertions, 5 deletions
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 */
}