[PATCH v2] sched/fair: Fix clearing of has_idle_cores flag

[PATCH v2] sched/fair: Fix clearing of has_idle_cores flag

[Gautham R. Shenoy]

From: "Gautham R. Shenoy" <ego@linux.vnet.ibm.com>

In commit 9fe1f127b913 ("sched/fair: Merge select_idle_core/cpu()"),
in select_idle_cpu(), we check if an idle core is present in the LLC
of the target CPU via the flag "has_idle_cores". We look for the idle
core in select_idle_cores(). If select_idle_cores() isn't able to find
an idle core/CPU, we need to unset the has_idle_cores flag in the LLC
of the target to prevent other CPUs from going down this route.

However, the current code is unsetting it in the LLC of the current
CPU instead of the target CPU. This patch fixes this issue.

Fixes: Commit 9fe1f127b913 ("sched/fair: Merge select_idle_core/cpu()")
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Reviewed-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
---
v1 --> v2 : Rebased against tip/sched/core

 kernel/sched/fair.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 1d75af1..6de1101 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6217,7 +6217,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool
 	}
 
 	if (has_idle_core)
-		set_idle_cores(this, false);
+		set_idle_cores(target, false);
 
 	if (sched_feat(SIS_PROP) && !has_idle_core) {
 		time = cpu_clock(this) - time;
-- 
1.9.4

[tip: sched/urgent] sched/fair: Fix clearing of has_idle_cores flag in select_idle_cpu()

[tip-bot2 for Gautham R. Shenoy]

The following commit has been merged into the sched/urgent branch of tip:

Commit-ID:     02dbb7246c5bbbbe1607ebdc546ba5c454a664b1
Gitweb:        https://git.kernel.org/tip/02dbb7246c5bbbbe1607ebdc546ba5c454a664b1
Author:        Gautham R. Shenoy <ego@linux.vnet.ibm.com>
AuthorDate:    Tue, 11 May 2021 20:46:09 +05:30
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Wed, 12 May 2021 10:41:28 +02:00

sched/fair: Fix clearing of has_idle_cores flag in select_idle_cpu()

In commit:

  9fe1f127b913 ("sched/fair: Merge select_idle_core/cpu()")

in select_idle_cpu(), we check if an idle core is present in the LLC
of the target CPU via the flag "has_idle_cores". We look for the idle
core in select_idle_cores(). If select_idle_cores() isn't able to find
an idle core/CPU, we need to unset the has_idle_cores flag in the LLC
of the target to prevent other CPUs from going down this route.

However, the current code is unsetting it in the LLC of the current
CPU instead of the target CPU. This patch fixes this issue.

Fixes: 9fe1f127b913 ("sched/fair: Merge select_idle_core/cpu()")
Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Reviewed-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Link: https://lore.kernel.org/r/1620746169-13996-1-git-send-email-ego@linux.vnet.ibm.com
---
 kernel/sched/fair.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 20aa234..3248e24 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6217,7 +6217,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool 
 	}
 
 	if (has_idle_core)
-		set_idle_cores(this, false);
+		set_idle_cores(target, false);
 
 	if (sched_feat(SIS_PROP) && !has_idle_core) {
 		time = cpu_clock(this) - time;

Re: [PATCH v2] sched/fair: Fix clearing of has_idle_cores flag

[Peter Zijlstra]

On Tue, May 11, 2021 at 08:46:09PM +0530, Gautham R. Shenoy wrote:
> From: "Gautham R. Shenoy" <ego@linux.vnet.ibm.com>
> 
> In commit 9fe1f127b913 ("sched/fair: Merge select_idle_core/cpu()"),
> in select_idle_cpu(), we check if an idle core is present in the LLC
> of the target CPU via the flag "has_idle_cores". We look for the idle
> core in select_idle_cores(). If select_idle_cores() isn't able to find
> an idle core/CPU, we need to unset the has_idle_cores flag in the LLC
> of the target to prevent other CPUs from going down this route.
> 
> However, the current code is unsetting it in the LLC of the current
> CPU instead of the target CPU. This patch fixes this issue.
> 
> Fixes: Commit 9fe1f127b913 ("sched/fair: Merge select_idle_core/cpu()")
> Acked-by: Mel Gorman <mgorman@techsingularity.net>
> Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
> Reviewed-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
> Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>

Thanks!