* [PATCH] x86/aperfmperf: use time_is_before_jiffies(a + b) to replace "jiffies - a > b" @ 2022-07-27 3:14 Yu Zhe 2022-07-27 16:00 ` Peter Zijlstra 0 siblings, 1 reply; 4+ messages in thread From: Yu Zhe @ 2022-07-27 3:14 UTC (permalink / raw) To: tglx, mingo, bp, dave.hansen, x86, hpa Cc: linux-kernel, kernel-janitors, liqiong, Yu Zhe time_is_before_jiffies deals with timer wrapping correctly. 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 ^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] x86/aperfmperf: use time_is_before_jiffies(a + b) to replace "jiffies - a > b" 2022-07-27 3:14 [PATCH] x86/aperfmperf: use time_is_before_jiffies(a + b) to replace "jiffies - a > b" Yu Zhe @ 2022-07-27 16:00 ` Peter Zijlstra 2022-07-28 2:55 ` Yu Zhe 0 siblings, 1 reply; 4+ messages in thread From: Peter Zijlstra @ 2022-07-27 16:00 UTC (permalink / raw) To: Yu Zhe Cc: tglx, mingo, bp, dave.hansen, x86, hpa, linux-kernel, kernel-janitors, liqiong 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. > > 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 > ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] x86/aperfmperf: use time_is_before_jiffies(a + b) to replace "jiffies - a > b" 2022-07-27 16:00 ` Peter Zijlstra @ 2022-07-28 2:55 ` Yu Zhe 2022-07-28 10:30 ` Peter Zijlstra 0 siblings, 1 reply; 4+ messages in thread From: Yu Zhe @ 2022-07-28 2:55 UTC (permalink / raw) To: Peter Zijlstra Cc: tglx, mingo, bp, dave.hansen, x86, hpa, linux-kernel, kernel-janitors, liqiong 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 >> > ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] x86/aperfmperf: use time_is_before_jiffies(a + b) to replace "jiffies - a > b" 2022-07-28 2:55 ` Yu Zhe @ 2022-07-28 10:30 ` Peter Zijlstra 0 siblings, 0 replies; 4+ messages in thread From: Peter Zijlstra @ 2022-07-28 10:30 UTC (permalink / raw) To: Yu Zhe Cc: tglx, mingo, bp, dave.hansen, x86, hpa, linux-kernel, kernel-janitors, liqiong On Thu, Jul 28, 2022 at 10:55:51AM +0800, Yu Zhe wrote: > 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. Now try the same with the existing code... ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2022-07-28 10:31 UTC | newest] Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2022-07-27 3:14 [PATCH] x86/aperfmperf: use time_is_before_jiffies(a + b) to replace "jiffies - a > b" Yu Zhe 2022-07-27 16:00 ` Peter Zijlstra 2022-07-28 2:55 ` Yu Zhe 2022-07-28 10:30 ` Peter Zijlstra
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