Note: While this is done in the context of select_idle_core(), I would not
expect it to be done like this. The intent is to illustrate how
idle_cpu_mask could be filtered before select_idle_cpus() scans
the rest of a domain or a wider scan was done across a cluster.
select_idle_core() potentially searches a number of CPUs for idle candidates
before select_idle_cpu() clears the mask and revisits the same CPUs. This
patch moves the initialisation of select_idle_mask to the top-level and
reuses the same mask across both select_idle_core and select_idle_cpu.
select_idle_smt() is left alone as the cost of checking one SMT sibling
is marginal relative to calling __clear_cpumask_cpu() for evey CPU
visited by select_idle_core().
Signed-off-by: Mel Gorman <mgor...@techsingularity.net>
---
kernel/sched/fair.c | 29 ++++++++++++++++-------------
1 file changed, 16 insertions(+), 13 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index cd95daf9f53e..af2e108c20c0 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6096,10 +6096,9 @@ void __update_idle_core(struct rq *rq)
* sd_llc->shared->has_idle_cores and enabled through update_idle_core() above.
*/
static int select_idle_core(struct task_struct *p, struct sched_domain *sd,
- int target, int nr)
+ int target, int nr, struct cpumask *cpus)
{
int idle_candidate = -1;
- struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_idle_mask);
int core, cpu;
if (!static_branch_likely(&sched_smt_present))
@@ -6108,9 +6107,6 @@ static int select_idle_core(struct task_struct *p, struct
sched_domain *sd,
if (!test_idle_cores(target, false))
return -1;
- cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
- __cpumask_clear_cpu(target, cpus);
-
for_each_cpu_wrap(core, cpus, target) {
bool idle = true;
@@ -6175,7 +6171,7 @@ static int select_idle_smt(struct task_struct *p, struct
sched_domain *sd, int t
#else /* CONFIG_SCHED_SMT */
static inline int select_idle_core(struct task_struct *p, struct sched_domain
*sd,
- int target, int nr)
+ int target, int nr, struct cpumask
*cpus)
{
return -1;
}
@@ -6193,14 +6189,10 @@ static inline int select_idle_smt(struct task_struct
*p, struct sched_domain *sd
* average idle time for this rq (as found in rq->avg_idle).
*/
static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd,
- int target, int nr)
+ int target, int nr, struct cpumask *cpus)
{
- struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_idle_mask);
int cpu;
- cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
- __cpumask_clear_cpu(target, cpus);
-
for_each_cpu_wrap(cpu, cpus, target) {
schedstat_inc(this_rq()->sis_scanned);
if (!--nr)
@@ -6260,6 +6252,7 @@ static inline bool asym_fits_capacity(int task_util, int
cpu)
static int select_idle_sibling(struct task_struct *p, int prev, int target)
{
struct sched_domain *sd, *this_sd;
+ struct cpumask *cpus_visited;
unsigned long task_util;
int i, recent_used_cpu, depth;
u64 time;
@@ -6358,13 +6351,23 @@ static int select_idle_sibling(struct task_struct *p,
int prev, int target)
depth = sis_search_depth(sd, this_sd);
+ /*
+ * Init the select_idle_mask. select_idle_core() will mask
+ * out the CPUs that have already been limited to limit the
+ * search in select_idle_cpu(). Further clearing is not
+ * done as select_idle_smt checks only one CPU.
+ */
+ cpus_visited = this_cpu_cpumask_var_ptr(select_idle_mask);
+ cpumask_and(cpus_visited, sched_domain_span(sd), p->cpus_ptr);
+ __cpumask_clear_cpu(target, cpus_visited);
+
schedstat_inc(this_rq()->sis_domain_search);
- i = select_idle_core(p, sd, target, depth);
+ i = select_idle_core(p, sd, target, depth, cpus_visited);
if ((unsigned)i < nr_cpumask_bits)
return i;
time = cpu_clock(smp_processor_id());
- i = select_idle_cpu(p, sd, target, depth);
+ i = select_idle_cpu(p, sd, target, depth, cpus_visited);
if ((unsigned)i < nr_cpumask_bits)
goto acct_cost;
--
2.26.2
