linux-kernel - [PATCH v2] sched/fair: Fix clearing of has_idle

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Date:   Tue, 11 May 2021 20:46:09 +0530
From:   "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
To:     Mel Gorman <mgorman@...hsingularity.net>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:     linux-kernel@...r.kernel.org,
        "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
Subject: [PATCH v2] sched/fair: Fix clearing of has_idle_cores flag

From: "Gautham R. Shenoy" <ego@...ux.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@...hsingularity.net>
Reviewed-by: Vincent Guittot <vincent.guittot@...aro.org>
Reviewed-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Signed-off-by: Gautham R. Shenoy <ego@...ux.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