netdev - [PATCH 12/16] time: optimize tick_check

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Message-Id: <20220718192844.1805158-13-yury.norov@gmail.com>
Date:   Mon, 18 Jul 2022 12:28:40 -0700
From:   Yury Norov <yury.norov@...il.com>
To:     linux-kernel@...r.kernel.org,
        Alexander Lobakin <alexandr.lobakin@...el.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Alexey Klimov <aklimov@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Ben Segall <bsegall@...gle.com>,
        Christoph Lameter <cl@...ux.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Dennis Zhou <dennis@...nel.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Eric Dumazet <edumazet@...gle.com>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Ingo Molnar <mingo@...hat.com>,
        Isabella Basso <isabbasso@...eup.net>,
        John Fastabend <john.fastabend@...il.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Juergen Gross <jgross@...e.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        KP Singh <kpsingh@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Martin KaFai Lau <kafai@...com>,
        Mel Gorman <mgorman@...e.de>, Miroslav Benes <mbenes@...e.cz>,
        Nathan Chancellor <nathan@...nel.org>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Song Liu <songliubraving@...com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Tejun Heo <tj@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Valentin Schneider <vschneid@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Vlastimil Babka <vbabka@...e.cz>, Yonghong Song <yhs@...com>,
        Yury Norov <yury.norov@...il.com>, linux-mm@...ck.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org
Subject: [PATCH 12/16] time: optimize tick_check_percpu()

tick_check_percpu() calls cpumask_equal() even if
curdev->cpumask == cpumask_of(cpu). Fix it.

Caught with CONFIG_DEBUG_BITMAP:
[    0.077622] Call trace:
[    0.077637]  __bitmap_check_params+0x144/0x250
[    0.077675]  tick_check_replacement+0xac/0x320
[    0.077716]  tick_check_new_device+0x50/0x110
[    0.077747]  clockevents_register_device+0x74/0x1c0
[    0.077779]  dummy_timer_starting_cpu+0x6c/0x80
[    0.077817]  cpuhp_invoke_callback+0x104/0x20c
[    0.077856]  cpuhp_invoke_callback_range+0x70/0xf0
[    0.077890]  notify_cpu_starting+0xac/0xcc
[    0.077921]  secondary_start_kernel+0xe4/0x154
[    0.077951]  __secondary_switched+0xa0/0xa4
[    0.077992] ---[ end trace 0000000000000000 ]---
[    0.078021] b1:	ffffbfec4703b890
[    0.078031] b2:	ffffbfec4703b890
[    0.078043] b3:	0
[    0.078052] nbits:	256
[    0.078065] start:	0
[    0.078075] off:	0
[    0.078086] Bitmap: parameters check failed
[    0.078095] include/linux/bitmap.h [419]: bitmap_equal

Signed-off-by: Yury Norov <yury.norov@...il.com>
---
 kernel/time/tick-common.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
index fdd5ae1a074b..7205f76f8d10 100644
--- a/kernel/time/tick-common.c
+++ b/kernel/time/tick-common.c
@@ -290,13 +290,15 @@ static bool tick_check_percpu(struct clock_event_device *curdev,
 {
 	if (!cpumask_test_cpu(cpu, newdev->cpumask))
 		return false;
-	if (cpumask_equal(newdev->cpumask, cpumask_of(cpu)))
+	if (newdev->cpumask == cpumask_of(cpu) ||
+			cpumask_equal(newdev->cpumask, cpumask_of(cpu)))
 		return true;
 	/* Check if irq affinity can be set */
 	if (newdev->irq >= 0 && !irq_can_set_affinity(newdev->irq))
 		return false;
 	/* Prefer an existing cpu local device */
-	if (curdev && cpumask_equal(curdev->cpumask, cpumask_of(cpu)))
+	if (curdev && (curdev->cpumask == cpumask_of(cpu) ||
+			cpumask_equal(curdev->cpumask, cpumask_of(cpu))))
 		return false;
 	return true;
 }
-- 
2.34.1