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Subject[RFC PATCH 2/9] sched: add search limit as per latency-nice
Date
Put upper and lower limit on CPU search in select_idle_cpu. The lower limit
is set to amount of CPUs in a core while upper limit is derived from the
latency-nice of the thread. This ensures for any architecture we will
usually search beyond a core. Changing the latency-nice value by user will
change the search cost making it appropriate for given workload.

Signed-off-by: subhra mazumdar <subhra.mazumdar@oracle.com>
---
kernel/sched/fair.c | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index b08d00c..c31082d 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6188,7 +6188,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
u64 avg_cost, avg_idle;
u64 time, cost;
s64 delta;
- int cpu, nr = INT_MAX;
+ int cpu, floor, nr = INT_MAX;

this_sd = rcu_dereference(*this_cpu_ptr(&sd_llc));
if (!this_sd)
@@ -6205,11 +6205,12 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
return -1;

if (sched_feat(SIS_PROP)) {
- u64 span_avg = sd->span_weight * avg_idle;
- if (span_avg > 4*avg_cost)
- nr = div_u64(span_avg, avg_cost);
- else
- nr = 4;
+ floor = cpumask_weight(topology_sibling_cpumask(target));
+ if (floor < 2)
+ floor = 2;
+ nr = (p->latency_nice * sd->span_weight) / LATENCY_NICE_MAX;
+ if (nr < floor)
+ nr = floor;
}

time = local_clock();
--
2.9.3
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