linux-kernel - [PATCH] sched/fair: Fix unsetting of "has_idle

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Message-Id: <1619456652-19143-1-git-send-email-ego@linux.vnet.ibm.com>
Date:   Mon, 26 Apr 2021 22:34:12 +0530
From:   "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
To:     Mel Gorman <mgorman@...hsingularity.net>,
        "Peter Zijlstra (Intel)" <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] sched/fair: Fix unsetting 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()")
Cc: Mel Gorman <mgorman@...hsingularity.net>
Signed-off-by: Gautham R. Shenoy <ego@...ux.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