linux-kernel - [PATCH] sched/cpuacct: show only present CPUs to userspace

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Message-Id: <20241017102138.92504-1-aleksandr.mikhalitsyn@canonical.com>
Date: Thu, 17 Oct 2024 12:21:38 +0200
From: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>
To: mingo@...hat.com
Cc: James Morse <james.morse@....com>,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	Gavin Shan <gshan@...hat.com>,
	"Russell King (Oracle)" <rmk+kernel@...linux.org.uk>,
	Thomas Gleixner <tglx@...utronix.de>,
	Simon Deziel <simon.deziel@...onical.com>,
	Alexander Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>,
	Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] sched/cpuacct: show only present CPUs to userspace

After commit b0c69e1214bc ("drivers: base: Use present CPUs in GENERIC_CPU_DEVICES")
changed which CPUs are shown in /sys/devices/system/cpu/ (only "present" ones)
it also makes sense to change cpuacct cgroupv1 code not to report CPUs
which are not present in the system as it confuses userspace.
Let's make it consistent.

A configuration when #(present CPUs) < #(possible CPUs) is easy to get with:
qemu-system-x86_64
	-smp 3,maxcpus=12 \
	...

Cc: James Morse <james.morse@....com>
Cc: Jonathan Cameron <Jonathan.Cameron@...wei.com>
Cc: Gavin Shan <gshan@...hat.com>
Cc: "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>
Cc: Thomas Gleixner <tglx@...utronix.de>
Reported-by: Simon Deziel <simon.deziel@...onical.com>
Closes: https://github.com/canonical/lxd/issues/13324
Co-developed-by: Simon Deziel <simon.deziel@...onical.com>
Signed-off-by: Simon Deziel <simon.deziel@...onical.com>
Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>
---
 kernel/sched/cpuacct.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/cpuacct.c b/kernel/sched/cpuacct.c
index 0de9dda09949..0f07fbfdb20e 100644
--- a/kernel/sched/cpuacct.c
+++ b/kernel/sched/cpuacct.c
@@ -213,7 +213,7 @@ static int __cpuacct_percpu_seq_show(struct seq_file *m,
 	u64 percpu;
 	int i;
 
-	for_each_possible_cpu(i) {
+	for_each_present_cpu(i) {
 		percpu = cpuacct_cpuusage_read(ca, i, index);
 		seq_printf(m, "%llu ", (unsigned long long) percpu);
 	}
@@ -247,7 +247,7 @@ static int cpuacct_all_seq_show(struct seq_file *m, void *V)
 		seq_printf(m, " %s", cpuacct_stat_desc[index]);
 	seq_puts(m, "\n");
 
-	for_each_possible_cpu(cpu) {
+	for_each_present_cpu(cpu) {
 		seq_printf(m, "%d", cpu);
 		for (index = 0; index < CPUACCT_STAT_NSTATS; index++)
 			seq_printf(m, " %llu",
-- 
2.34.1