@@ -714,6 +714,10 @@ do { \
P(sched_goidle);
P(ttwu_count);
P(ttwu_local);
+ P(sis_search);
+ P(sis_domain_search);
+ P(sis_scanned);
+ P(sis_failed);
}
#undef P
@@ -6081,6 +6081,7 @@ static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int
bool idle = true;
for_each_cpu(cpu, cpu_smt_mask(core)) {
+ schedstat_inc(this_rq()->sis_scanned);
if (!available_idle_cpu(cpu)) {
idle = false;
break;
@@ -6112,6 +6113,7 @@ static int select_idle_smt(struct task_struct *p, struct sched_domain *sd, int t
return -1;
for_each_cpu(cpu, cpu_smt_mask(target)) {
+ schedstat_inc(this_rq()->sis_scanned);
if (!cpumask_test_cpu(cpu, p->cpus_ptr) ||
!cpumask_test_cpu(cpu, sched_domain_span(sd)))
continue;
@@ -6177,6 +6179,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
for_each_cpu_wrap(cpu, cpus, target) {
+ schedstat_inc(this_rq()->sis_scanned);
if (!--nr)
return -1;
if (available_idle_cpu(cpu) || sched_idle_cpu(cpu))
@@ -6240,6 +6243,15 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
unsigned long task_util;
int i, recent_used_cpu;
+ schedstat_inc(this_rq()->sis_search);
+
+ /*
+ * Checking if prev, target and recent is treated as one scan. A
+ * perfect hit on one of those is considered 100% efficiency.
+ * Further scanning impairs efficiency.
+ */
+ schedstat_inc(this_rq()->sis_scanned);
+
/*
* On asymmetric system, update task utilization because we will check
* that the task fits with cpu's capacity.
@@ -6315,6 +6327,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
if (!sd)
return target;
+ schedstat_inc(this_rq()->sis_domain_search);
i = select_idle_core(p, sd, target);
if ((unsigned)i < nr_cpumask_bits)
return i;
@@ -6327,6 +6340,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
if ((unsigned)i < nr_cpumask_bits)
return i;
+ schedstat_inc(this_rq()->sis_failed);
return target;
}
@@ -1049,6 +1049,12 @@ struct rq {
/* try_to_wake_up() stats */
unsigned int ttwu_count;
unsigned int ttwu_local;
+
+ /* select_idle_sibling stats */
+ unsigned int sis_search;
+ unsigned int sis_domain_search;
+ unsigned int sis_scanned;
+ unsigned int sis_failed;
#endif
#ifdef CONFIG_CPU_IDLE
@@ -10,7 +10,7 @@
* Bump this up when changing the output format or the meaning of an existing
* format, so that tools can adapt (or abort)
*/
-#define SCHEDSTAT_VERSION 15
+#define SCHEDSTAT_VERSION 16
static int show_schedstat(struct seq_file *seq, void *v)
{
@@ -30,12 +30,14 @@ static int show_schedstat(struct seq_file *seq, void *v)
/* runqueue-specific stats */
seq_printf(seq,
- "cpu%d %u 0 %u %u %u %u %llu %llu %lu",
+ "cpu%d %u 0 %u %u %u %u %llu %llu %lu %u %u %u %u",
cpu, rq->yld_count,
rq->sched_count, rq->sched_goidle,
rq->ttwu_count, rq->ttwu_local,
rq->rq_cpu_time,
- rq->rq_sched_info.run_delay, rq->rq_sched_info.pcount);
+ rq->rq_sched_info.run_delay, rq->rq_sched_info.pcount,
+ rq->sis_search, rq->sis_domain_search,
+ rq->sis_scanned, rq->sis_failed);
seq_printf(seq, "\n");
select_idle_sibling is an important path that finds a nearby idle CPU on wakeup. As it is examining other CPUs state, it can be expensive in terms of cache usage. This patch tracks the search efficiency if schedstats are enabled. In general, this is only useful for kernel developers but schedstats are typically disabled by default so it is convenient for development and mostly free otherwise. It is not required that this patch be merged with the series but if we are looking at time or search complexity, the stats generate hard data on what the search costs actually are. SIS Search: Number of calls to select_idle_sibling SIS Domain Search: Number of times the domain was searched because the fast path failed. SIS Scanned: Generally the number of runqueues scanned but the fast path counts as 1 regardless of the values for target, prev and recent. SIS Domain Scanned: Number of runqueues scanned during a search of the LLC domain. SIS Failures: Number of SIS calls that failed to find an idle CPU SIS Search Efficiency: A ratio expressed as a percentage of runqueues scanned versus idle CPUs found. A 100% efficiency indicates that the target, prev or recent CPU of a task was idle at wakeup. The lower the efficiency, the more runqueues were scanned before an idle CPU was found. SIS Domain Search Efficiency: Similar, except only for the slower SIS patch. SIS Fast Success Rate: Percentage of SIS that used target, prev or recent CPUs. SIS Success rate: Percentage of scans that found an idle CPU. Signed-off-by: Mel Gorman <mgorman@techsingularity.net> --- kernel/sched/debug.c | 4 ++++ kernel/sched/fair.c | 14 ++++++++++++++ kernel/sched/sched.h | 6 ++++++ kernel/sched/stats.c | 8 +++++--- 4 files changed, 29 insertions(+), 3 deletions(-)