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Message-Id: <1490205470-10249-1-git-send-email-srikar@linux.vnet.ibm.com>
Date: Wed, 22 Mar 2017 23:27:50 +0530
From: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To: Ingo Molnar <mingo@...nel.org>,
Peter Zijlstra <peterz@...radead.org>
Cc: Vincent Guittot <vincent.guittot@...aro.org>,
Mike Galbraith <efault@....de>,
Thomas Gleixner <tglx@...utronix.de>,
LKML <linux-kernel@...r.kernel.org>,
Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Subject: [PATCH] sched: Prefer sibiling only if local group is under-utilized
If the child domain prefers tasks to go siblings, the local group could
end up pulling tasks to itself even if the local group is almost equally
loaded as the source group.
Lets assume a 4 core,smt==2 machine running 5 thread ebizzy workload.
Everytime, local group has capacity and source group has atleast 2 threads,
local group tries to pull the task. This causes the threads to constantly
move between different cores. This is even more profound if the cores have
more threads, like in Power 8, smt 8 mode.
Fix this by only allowing local group to pull a task, if the source group
has more number of tasks than the local group.
Signed-off-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
---
Here are the relevant perf stat numbers of a 22 core,smt 8 Power 8 machine.
Without patch:
Performance counter stats for 'ebizzy -t 22 -S 100' (5 runs):
1,440 context-switches # 0.001 K/sec ( +- 1.26% )
366 cpu-migrations # 0.000 K/sec ( +- 5.58% )
3,933 page-faults # 0.002 K/sec ( +- 11.08% )
Performance counter stats for 'ebizzy -t 48 -S 100' (5 runs):
6,287 context-switches # 0.001 K/sec ( +- 3.65% )
3,776 cpu-migrations # 0.001 K/sec ( +- 4.84% )
5,702 page-faults # 0.001 K/sec ( +- 9.36% )
Performance counter stats for 'ebizzy -t 96 -S 100' (5 runs):
8,776 context-switches # 0.001 K/sec ( +- 0.73% )
2,790 cpu-migrations # 0.000 K/sec ( +- 0.98% )
10,540 page-faults # 0.001 K/sec ( +- 3.12% )
With patch:
Performance counter stats for 'ebizzy -t 22 -S 100' (5 runs):
1,133 context-switches # 0.001 K/sec ( +- 4.72% )
123 cpu-migrations # 0.000 K/sec ( +- 3.42% )
3,858 page-faults # 0.002 K/sec ( +- 8.52% )
Performance counter stats for 'ebizzy -t 48 -S 100' (5 runs):
2,169 context-switches # 0.000 K/sec ( +- 6.19% )
189 cpu-migrations # 0.000 K/sec ( +- 12.75% )
5,917 page-faults # 0.001 K/sec ( +- 8.09% )
Performance counter stats for 'ebizzy -t 96 -S 100' (5 runs):
5,333 context-switches # 0.001 K/sec ( +- 5.91% )
506 cpu-migrations # 0.000 K/sec ( +- 3.35% )
10,792 page-faults # 0.001 K/sec ( +- 7.75% )
---
kernel/sched/fair.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 6559d19..a6dd010 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7496,6 +7496,7 @@ static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sd
{
struct sched_domain *child = env->sd->child;
struct sched_group *sg = env->sd->groups;
+ struct sg_lb_stats *local = &sds->local_stat;
struct sg_lb_stats tmp_sgs;
int load_idx, prefer_sibling = 0;
bool overload = false;
@@ -7512,7 +7513,7 @@ static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sd
local_group = cpumask_test_cpu(env->dst_cpu, sched_group_cpus(sg));
if (local_group) {
sds->local = sg;
- sgs = &sds->local_stat;
+ sgs = local;
if (env->idle != CPU_NEWLY_IDLE ||
time_after_eq(jiffies, sg->sgc->next_update))
@@ -7536,8 +7537,8 @@ static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sd
* the tasks on the system).
*/
if (prefer_sibling && sds->local &&
- group_has_capacity(env, &sds->local_stat) &&
- (sgs->sum_nr_running > 1)) {
+ group_has_capacity(env, local) &&
+ (sgs->sum_nr_running > local->sum_nr_running + 1)) {
sgs->group_no_capacity = 1;
sgs->group_type = group_classify(sg, sgs);
}
--
1.8.3.1
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