Messages in this thread Patch in this message | | | From | Xiongfeng Wang <> | Subject | [RFC PATCH] timer: Fix bucket_expiry calculation | Date | Wed, 12 May 2021 20:15:29 +0800 |
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When I use schedule_timeout(5) to put a process into sleep on my machine with HZ = 100. It always sleep about 60ms. I enable the timer trace and find out, when the timer_list expires, 'now' is always equal to 'expires + 1'. I print 'base->next_expiry' in '__run_timers' and find out 'next_expiry' is always equal to 'expires + 1';
my_test_thread-1230 [001] d... 382.627089: timer_start: timer=000000004ec021c9 function=process_timeout expires=4294975072 [timeout=5] cpu=1 idx=33 flags= <idle>-0 [001] ..s. 382.687082: run_timer_softirq: jiffies 4294975073 next_expiry 4294975073 <idle>-0 [001] ..s. 382.687083: timer_expire_entry: timer=000000004ec021c9 function=process_timeout now=4294975073 baseclk=4294975073 my_test_thread-1230 [001] d... 382.687089: timer_start: timer=000000004ec021c9 function=process_timeout expires=4294975078 [timeout=5] cpu=1 idx=39 flags= <idle>-0 [001] ..s. 382.747083: run_timer_softirq: jiffies 4294975079 next_expiry 4294975079 <idle>-0 [001] ..s. 382.747084: timer_expire_entry: timer=000000004ec021c9 function=process_timeout now=4294975079 baseclk=4294975079
It is because we use the following equation to calculate bucket_expiry.
bucket_expiry = ((expires + LVL_GRAN(lvl)) >> LVL_SHIFT(lvl)) << LVL_SHIFT(lvl)
'bucket_expiry' is equal to 'expires + 1' when lvl = 0. So modify the equation as follows to fix the issue.
bucket_expiry = ((expires + LVL_GRAN(lvl) - 1) >> LVL_SHIFT(lvl)) << LVL_SHIFT(lvl)
Signed-off-by: Xiongfeng Wang <wangxiongfeng2@huawei.com> --- kernel/time/timer.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/time/timer.c b/kernel/time/timer.c index d111adf..a6a26da 100644 --- a/kernel/time/timer.c +++ b/kernel/time/timer.c @@ -501,7 +501,7 @@ static inline unsigned calc_index(unsigned long expires, unsigned lvl, * * Round up with level granularity to prevent this. */ - expires = (expires + LVL_GRAN(lvl)) >> LVL_SHIFT(lvl); + expires = (expires + LVL_GRAN(lvl) - 1) >> LVL_SHIFT(lvl); *bucket_expiry = expires << LVL_SHIFT(lvl); return LVL_OFFS(lvl) + (expires & LVL_MASK); } -- 1.7.12.4
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