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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2014-06-04 22:46:03 +0200
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2014-07-09 18:15:02 +0200
commitc0f489d2c6fec8994c642c2ec925eb858727dc7b (patch)
treee72f709231a498626a149ef676bd60ff0e1b26c3 /kernel/time/tick-sched.c
parentrcu: Simplify priority boosting by putting rt_mutex in rcu_node (diff)
downloadlinux-c0f489d2c6fec8994c642c2ec925eb858727dc7b.tar.xz
linux-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/time/tick-sched.c')
-rw-r--r--kernel/time/tick-sched.c10
1 files changed, 10 insertions, 0 deletions
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 6558b7ac112d..f784d83e29f1 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 housekeeping_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(&housekeeping_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(housekeeping_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(&housekeeping_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(housekeeping_mask);
+ cpumask_set_cpu(smp_processor_id(), housekeeping_mask);
tick_nohz_full_running = true;
#endif
return err;