Messages in this thread | | | Subject | Re: [PATCH] x86/aperfmperf: use time_is_before_jiffies(a + b) to replace "jiffies - a > b" | From | Yu Zhe <> | Date | Thu, 28 Jul 2022 10:55:51 +0800 |
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在 2022年07月28日 00:00, Peter Zijlstra 写道:
> On Wed, Jul 27, 2022 at 11:14:05AM +0800, Yu Zhe wrote: >> time_is_before_jiffies deals with timer wrapping correctly. > Please explain how the current code does not.
1. If the timer wrap changes in the future you won't have to alter your code.
2. unsigned long ut;
ut = ULONG_MAX + 4;
printf("time_after(ut, ULONG_MAX), ut:%d, %d --> %d\n", ut, time_after(ut, ULONG_MAX), (ULONG_MAX - ut) < 0);
In this case, time_after returns true, it's correct.
>> Signed-off-by: Yu Zhe <yuzhe@nfschina.com> >> --- >> arch/x86/kernel/cpu/aperfmperf.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/arch/x86/kernel/cpu/aperfmperf.c b/arch/x86/kernel/cpu/aperfmperf.c >> index 1f60a2b27936..22e0bac3fffe 100644 >> --- a/arch/x86/kernel/cpu/aperfmperf.c >> +++ b/arch/x86/kernel/cpu/aperfmperf.c >> @@ -423,7 +423,7 @@ unsigned int arch_freq_get_on_cpu(int cpu) >> * Bail on invalid count and when the last update was too long ago, >> * which covers idle and NOHZ full CPUs. >> */ >> - if (!mcnt || (jiffies - last) > MAX_SAMPLE_AGE) >> + if (!mcnt || time_is_before_jiffies(last + MAX_SAMPLE_AGE)) >> goto fallback; >> >> return div64_u64((cpu_khz * acnt), mcnt); >> -- >> 2.11.0 >> >
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