linux-kernel - [tip: sched/core] sched/fair: Exclude the current CPU from find_new

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Message-ID: <160396870806.397.17543198051603219100.tip-bot2@tip-bot2>
Date:   Thu, 29 Oct 2020 10:51:48 -0000
From:   "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        x86 <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: [tip: sched/core] sched/fair: Exclude the current CPU from find_new_ilb()

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

Commit-ID:     45da7a2b0af8fa29dff2e6ba8926322068350fce
Gitweb:        https://git.kernel.org/tip/45da7a2b0af8fa29dff2e6ba8926322068350fce
Author:        Peter Zijlstra <peterz@...radead.org>
AuthorDate:    Tue, 18 Aug 2020 10:48:17 +02:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Thu, 29 Oct 2020 11:00:30 +01:00

sched/fair: Exclude the current CPU from find_new_ilb()

It is possible for find_new_ilb() to select the current CPU, however,
this only happens from newidle balancing, in which case need_resched()
will be true, and consequently nohz_csd_func() will not trigger the
softirq.

Exclude the current CPU from becoming an ILB target.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 kernel/sched/fair.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index b9368d1..cd9a37c 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -10056,6 +10056,10 @@ static inline int find_new_ilb(void)
 
 	for_each_cpu_and(ilb, nohz.idle_cpus_mask,
 			      housekeeping_cpumask(HK_FLAG_MISC)) {
+
+		if (ilb == smp_processor_id())
+			continue;
+
 		if (idle_cpu(ilb))
 			return ilb;
 	}