linux-kernel - [PATCH 11/16] time: optimize tick_check

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Date:   Mon, 18 Jul 2022 12:28:39 -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 11/16] time: optimize tick_check_preferred()

tick_check_preferred() calls cpumask_equal() even if
curdev->cpumask == newdev->cpumask. Fix it.

Caught with CONFIG_DEBUG_BITMAP:
[    0.079109] Call trace:
[    0.079124]  __bitmap_check_params+0x144/0x250
[    0.079161]  tick_check_replacement+0x1a4/0x320
[    0.079203]  tick_check_new_device+0x50/0x110
[    0.079237]  clockevents_register_device+0x74/0x1c0
[    0.079268]  dummy_timer_starting_cpu+0x6c/0x80
[    0.079310]  cpuhp_invoke_callback+0x104/0x20c
[    0.079353]  cpuhp_invoke_callback_range+0x70/0xf0
[    0.079401]  notify_cpu_starting+0xac/0xcc
[    0.079434]  secondary_start_kernel+0xe4/0x154
[    0.079471]  __secondary_switched+0xa0/0xa4
[    0.079516] ---[ end trace 0000000000000000 ]---
[    0.079542] b1:	ffffbfec4703b890
[    0.079553] b2:	ffffbfec4703b890
[    0.079566] b3:	0
[    0.079576] nbits:	256
[    0.079588] start:	0
[    0.079598] off:	0
[    0.079609] Bitmap: parameters check failed
[    0.079619] include/linux/bitmap.h [419]: bitmap_equal

Signed-off-by: Yury Norov <yury.norov@...il.com>
---
 kernel/time/tick-common.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
index 46789356f856..fdd5ae1a074b 100644
--- a/kernel/time/tick-common.c
+++ b/kernel/time/tick-common.c
@@ -316,9 +316,13 @@ static bool tick_check_preferred(struct clock_event_device *curdev,
 	 * Use the higher rated one, but prefer a CPU local device with a lower
 	 * rating than a non-CPU local device
 	 */
-	return !curdev ||
-		newdev->rating > curdev->rating ||
-	       !cpumask_equal(curdev->cpumask, newdev->cpumask);
+	if (!curdev || newdev->rating > curdev->rating)
+		return true;
+
+	if (newdev->cpumask == curdev->cpumask)
+		return false;
+
+	return !cpumask_equal(curdev->cpumask, newdev->cpumask);
 }
 
 /*
-- 
2.34.1