Re: [PATCH v3 5/7] sched: SIS_CORE to disable idle core search

[Subhra Mazumdar]

On 7/4/19 6:04 PM, Parth Shah wrote:

Same experiment with hackbench and with perf analysis shows increase in L1
cache miss rate with these patches
(Lower is better)
                           Baseline(%)   Patch(%)
  ----------------------- ------------- -----------
   Total Cache miss rate         17.01   19(-11%)
   L1 icache miss rate            5.45   6.7(-22%)



So is is possible for idle_cpu search to try checking target_cpu first and
then goto sliding window if not found.
Below diff works as expected in IBM POWER9 system and resolves the problem
of far wakeup upto large extent.

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index ff2e9b5c3ac5..fae035ce1162 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6161,6 +6161,7 @@ static int select_idle_cpu(struct task_struct *p, struct 
sched_domain *sd, int t
         u64 time, cost;
         s64 delta;
         int cpu, limit, floor, target_tmp, nr = INT_MAX;
+       struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_idle_mask);

this_sd = rcu_dereference(*this_cpu_ptr(&sd_llc));

         if (!this_sd)
@@ -6198,16 +6199,22 @@ static int select_idle_cpu(struct task_struct *p, 
struct sched_domain *sd, int t

time = local_clock(); - for_each_cpu_wrap(cpu, sched_domain_span(sd), target_tmp) {

+       cpumask_and(cpus, sched_domain_span(sd), &p->cpus_allowed);
+       for_each_cpu_wrap(cpu, cpu_smt_mask(target), target) {
+               __cpumask_clear_cpu(cpu, cpus);
+               if (available_idle_cpu(cpu))
+                       goto idle_cpu_exit;
+       }
+
+       for_each_cpu_wrap(cpu, cpus, target_tmp) {
                 per_cpu(next_cpu, target) = cpu;
                 if (!--nr)
                         return -1;
-               if (!cpumask_test_cpu(cpu, &p->cpus_allowed))
-                       continue;
                 if (available_idle_cpu(cpu))
                         break;
         }

+idle_cpu_exit:

         time = local_clock() - time;
         cost = this_sd->avg_scan_cost;
         delta = (s64)(time - cost) / 8;



Best,
Parth

How about calling select_idle_smt before select_idle_cpu from
select_idle_sibling? That should have the same effect.