[PATCH 11/16] time: optimize tick_check_preferred()

Yury Norov
2022-07-18T19:30:32Z

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@gmail.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