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| author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2014-06-04 13:46:03 -0700 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2014-07-09 09:15:02 -0700 |
| commit | c0f489d2c6fec8994c642c2ec925eb858727dc7b (patch) | |
| tree | e72f709231a498626a149ef676bd60ff0e1b26c3 /kernel/rcu/tree_plugin.h | |
| parent | abaa93d9e1de2c29297e69ddba8ddd38f15064cf (diff) | |
| download | lwn-c0f489d2c6fec8994c642c2ec925eb858727dc7b.tar.gz lwn-c0f489d2c6fec8994c642c2ec925eb858727dc7b.zip | |
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/tree_plugin.h')
| -rw-r--r-- | kernel/rcu/tree_plugin.h | 14 |
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 */ } |