[PATCH] sched/fair: Fix unsetting of "has_idle_cores" flag

[PATCH] sched/fair: Fix unsetting 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()")
Cc: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Gautham R. Shenoy <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 794c2cb..5fb5020 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6171,7 +6171,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
 	}
 
 	if (smt)
-		set_idle_cores(this, false);
+		set_idle_cores(target, false);
 
 	if (sched_feat(SIS_PROP) && !smt) {
 		time = cpu_clock(this) - time;
-- 
1.9.4

Re: [PATCH] sched/fair: Fix unsetting of "has_idle_cores" flag

[Vincent Guittot]

On Mon, 26 Apr 2021 at 19:04, Gautham R. Shenoy <ego@linux.vnet.ibm.com> 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()")
> Cc: Mel Gorman <mgorman@techsingularity.net>
> Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>

Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>

> ---
>  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 794c2cb..5fb5020 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -6171,7 +6171,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
>         }
>
>         if (smt)
> -               set_idle_cores(this, false);
> +               set_idle_cores(target, false);
>
>         if (sched_feat(SIS_PROP) && !smt) {
>                 time = cpu_clock(this) - time;
> --
> 1.9.4
>

Re: [PATCH] sched/fair: Fix unsetting of "has_idle_cores" flag

[Mel Gorman]

On Mon, Apr 26, 2021 at 10:34:12PM +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()")
> Cc: Mel Gorman <mgorman@techsingularity.net>
> Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>

Acked-by: Mel Gorman <mgorman@techsingularity.net>

-- 
Mel Gorman
SUSE Labs

Re: [PATCH] sched/fair: Fix unsetting of "has_idle_cores" flag

[Gautham R Shenoy]

Peter, Ingo,

Pinging to check on this tiny fix :-)


On Mon, Apr 26, 2021 at 10:34:12PM +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()")
> Cc: Mel Gorman <mgorman@techsingularity.net>
> Signed-off-by: Gautham R. Shenoy <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 794c2cb..5fb5020 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -6171,7 +6171,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
>  	}
> 
>  	if (smt)
> -		set_idle_cores(this, false);
> +		set_idle_cores(target, false);
> 
>  	if (sched_feat(SIS_PROP) && !smt) {
>  		time = cpu_clock(this) - time;
> -- 
> 1.9.4
>