linux-kernel - [tip: sched/core] sched/nohz: Remove unnecessarily complex error handling pattern from find_new

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Message-ID: <169684717032.3135.17626767741431018350.tip-bot2@tip-bot2>
Date:   Mon, 09 Oct 2023 10:26:10 -0000
From:   "tip-bot2 for Ingo Molnar" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Ingo Molnar <mingo@...nel.org>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: sched/core] sched/nohz: Remove unnecessarily complex error
 handling pattern from find_new_ilb()

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

Commit-ID:     f4bb5705114530cd775a5a649b666755b3efe7aa
Gitweb:        https://git.kernel.org/tip/f4bb5705114530cd775a5a649b666755b3efe7aa
Author:        Ingo Molnar <mingo@...nel.org>
AuthorDate:    Fri, 06 Oct 2023 12:25:18 +02:00
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Mon, 09 Oct 2023 12:21:23 +02:00

sched/nohz: Remove unnecessarily complex error handling pattern from find_new_ilb()

find_new_ilb() returns nr_cpu_ids on failure - which is the usual
cpumask bitops return pattern, but is weird & unnecessary in this
context: not only is it a global variable, it it is a +1 out of
bounds CPU index and also has different signedness ...

Its only user, kick_ilb(), then checks the return against nr_cpu_ids
to decide to return. There's no other use.

So instead of this, use a standard -1 return on failure to find an
idle CPU, as the argument is signed already.

Signed-off-by: Ingo Molnar <mingo@...nel.org>
Reviewed-by: Joel Fernandes (Google) <joel@...lfernandes.org>
Link: https://lore.kernel.org/r/20231006102518.2452758-4-mingo@kernel.org
---
 kernel/sched/fair.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index f82b301..19bb4ac 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -11528,7 +11528,7 @@ static inline int find_new_ilb(void)
 			return ilb_cpu;
 	}
 
-	return nr_cpu_ids;
+	return -1;
 }
 
 /*
@@ -11549,8 +11549,7 @@ static void kick_ilb(unsigned int flags)
 		nohz.next_balance = jiffies+1;
 
 	ilb_cpu = find_new_ilb();
-
-	if (ilb_cpu >= nr_cpu_ids)
+	if (ilb_cpu < 0)
 		return;
 
 	/*