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sched/fair: Optimize find_idlest_group() 

find_idlest_group() now reads CPU's load_avg in two different ways.

Consolidate the function to read and use load_avg only once and simplify
the algorithm to only look for the group with lowest load_avg.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Morten.Rasmussen@arm.com
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: hdanton@sina.com
Cc: parth@linux.ibm.com
Cc: pauld@redhat.com
Cc: quentin.perret@arm.com
Cc: riel@surriel.com
Cc: srikar@linux.vnet.ibm.com
Cc: valentin.schneider@arm.com
Link: https://lkml.kernel.org/r/1571405198-27570-11-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
alistair/sunxi64-5.5-dsi
Vincent Guittot 2019-10-18 15:26:37 +02:00 committed by Ingo Molnar
parent 11f10e5420
commit fc1273f4ce
1 changed files with 14 additions and 36 deletions
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50
kernel/sched/fair.c
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@ -5550,16 +5550,14 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p,
{
struct sched_group *idlest = NULL, *group = sd->groups;
struct sched_group *most_spare_sg = NULL;
unsigned long min_runnable_load = ULONG_MAX;
unsigned long this_runnable_load = ULONG_MAX;
unsigned long min_avg_load = ULONG_MAX, this_avg_load = ULONG_MAX;
unsigned long min_load = ULONG_MAX, this_load = ULONG_MAX;
unsigned long most_spare = 0, this_spare = 0;
int imbalance_scale = 100 + (sd->imbalance_pct-100)/2;
unsigned long imbalance = scale_load_down(NICE_0_LOAD) *
(sd->imbalance_pct-100) / 100;
do {
unsigned long load, avg_load, runnable_load;
unsigned long load;
unsigned long spare_cap, max_spare_cap;
int local_group;
int i;
@ -5576,15 +5574,11 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p,
* Tally up the load of all CPUs in the group and find
* the group containing the CPU with most spare capacity.
*/
avg_load = 0;
runnable_load = 0;
load = 0;
max_spare_cap = 0;
for_each_cpu(i, sched_group_span(group)) {
load = cpu_load(cpu_rq(i));
runnable_load += load;
avg_load += cfs_rq_load_avg(&cpu_rq(i)->cfs);
load += cpu_load(cpu_rq(i));
spare_cap = capacity_spare_without(i, p);
@ -5593,31 +5587,15 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p,
}
/* Adjust by relative CPU capacity of the group */
avg_load = (avg_load * SCHED_CAPACITY_SCALE) /
group->sgc->capacity;
runnable_load = (runnable_load * SCHED_CAPACITY_SCALE) /
load = (load * SCHED_CAPACITY_SCALE) /
group->sgc->capacity;
if (local_group) {
this_runnable_load = runnable_load;
this_avg_load = avg_load;
this_load = load;
this_spare = max_spare_cap;
} else {
if (min_runnable_load > (runnable_load + imbalance)) {
/*
* The runnable load is significantly smaller
* so we can pick this new CPU:
*/
min_runnable_load = runnable_load;
min_avg_load = avg_load;
idlest = group;
} else if ((runnable_load < (min_runnable_load + imbalance)) &&
(100*min_avg_load > imbalance_scale*avg_load)) {
/*
* The runnable loads are close so take the
* blocked load into account through avg_load:
*/
min_avg_load = avg_load;
if (load < min_load) {
min_load = load;
idlest = group;
}
@ -5658,18 +5636,18 @@ skip_spare:
* local domain to be very lightly loaded relative to the remote
* domains but "imbalance" skews the comparison making remote CPUs
* look much more favourable. When considering cross-domain, add
* imbalance to the runnable load on the remote node and consider
* staying local.
* imbalance to the load on the remote node and consider staying
* local.
*/
if ((sd->flags & SD_NUMA) &&
min_runnable_load + imbalance >= this_runnable_load)
min_load + imbalance >= this_load)
return NULL;
if (min_runnable_load > (this_runnable_load + imbalance))
if (min_load >= this_load + imbalance)
return NULL;
if ((this_runnable_load < (min_runnable_load + imbalance)) &&
(100*this_avg_load < imbalance_scale*min_avg_load))
if ((this_load < (min_load + imbalance)) &&
(100*this_load < imbalance_scale*min_load))
return NULL;
return idlest;