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Message-ID: <20231018155036.2314342-1-srikar@linux.vnet.ibm.com>
Date: Wed, 18 Oct 2023 21:20:35 +0530
From: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To: Ingo Molnar <mingo@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Steven Rostedt <rostedt@...dmis.org>,
Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
Valentin Schneider <vschneid@...hat.com>
Cc: LKML <linux-kernel@...r.kernel.org>,
Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Subject: [PATCH] sched/fair: Enable group_asym_packing in find_idlest_group
Current scheduler code doesn't handle SD_ASYM_PACKING in the
find_idlest_cpu path. On few architectures, like Powerpc, cache is at a
core. Moving threads across cores may end up in cache misses.
While asym_packing can be enabled above SMT level, enabling Asym packing
across cores could result in poorer performance due to cache misses.
However if the initial task placement via find_idlest_cpu does take
Asym_packing into consideration, then scheduler can avoid asym_packing
migrations. This will result in lesser migrations and better packing and
better overall performance.
Signed-off-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
---
kernel/sched/fair.c | 33 ++++++++++++++++++++++++++++++---
1 file changed, 30 insertions(+), 3 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index cb225921bbca..7164f79a3d13 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9931,11 +9931,13 @@ static int idle_cpu_without(int cpu, struct task_struct *p)
* @group: sched_group whose statistics are to be updated.
* @sgs: variable to hold the statistics for this group.
* @p: The task for which we look for the idlest group/CPU.
+ * @this_cpu: current cpu
*/
static inline void update_sg_wakeup_stats(struct sched_domain *sd,
struct sched_group *group,
struct sg_lb_stats *sgs,
- struct task_struct *p)
+ struct task_struct *p,
+ int this_cpu)
{
int i, nr_running;
@@ -9972,6 +9974,11 @@ static inline void update_sg_wakeup_stats(struct sched_domain *sd,
}
+ if (sd->flags & SD_ASYM_PACKING && sgs->sum_h_nr_running &&
+ sched_asym_prefer(group->asym_prefer_cpu, this_cpu)) {
+ sgs->group_asym_packing = 1;
+ }
+
sgs->group_capacity = group->sgc->capacity;
sgs->group_weight = group->group_weight;
@@ -10012,8 +10019,17 @@ static bool update_pick_idlest(struct sched_group *idlest,
return false;
break;
- case group_imbalanced:
case group_asym_packing:
+ if (sched_asym_prefer(group->asym_prefer_cpu, idlest->asym_prefer_cpu)) {
+ int busy_cpus = idlest_sgs->group_weight - idlest_sgs->idle_cpus;
+
+ busy_cpus -= (sgs->group_weight - sgs->idle_cpus);
+ if (busy_cpus >= 0)
+ return true;
+ }
+ return false;
+
+ case group_imbalanced:
case group_smt_balance:
/* Those types are not used in the slow wakeup path */
return false;
@@ -10080,7 +10096,7 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p, int this_cpu)
sgs = &tmp_sgs;
}
- update_sg_wakeup_stats(sd, group, sgs, p);
+ update_sg_wakeup_stats(sd, group, sgs, p, this_cpu);
if (!local_group && update_pick_idlest(idlest, &idlest_sgs, group, sgs)) {
idlest = group;
@@ -10112,6 +10128,17 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p, int this_cpu)
if (local_sgs.group_type > idlest_sgs.group_type)
return idlest;
+ if (idlest_sgs.group_type == group_asym_packing) {
+ if (sched_asym_prefer(idlest->asym_prefer_cpu, local->asym_prefer_cpu)) {
+ int busy_cpus = local_sgs.group_weight - local_sgs.idle_cpus;
+
+ busy_cpus -= (idlest_sgs.group_weight - idlest_sgs.idle_cpus);
+ if (busy_cpus >= 0)
+ return idlest;
+ }
+ return NULL;
+ }
+
switch (local_sgs.group_type) {
case group_overloaded:
case group_fully_busy:
--
2.31.1
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