Messages in this thread | | | Subject | Re: [BISECTED] "conservative" cpufreq governor broken | From | Eero Nurkkala <> | Date | Tue, 06 Oct 2009 15:36:49 +0300 |
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On Tue, 2009-10-06 at 13:22 +0200, ext Steven Noonan wrote: > On Tue, Oct 6, 2009 at 3:43 AM, Eero Nurkkala > <ext-eero.nurkkala@nokia.com> wrote: > > On Tue, 2009-10-06 at 12:22 +0200, ext Steven Noonan wrote: > >> > >> I would suspect you have to have CONFIG_NO_HZ enabled to be able to > >> reproduce the issue (considering the title of the bisected commit and > >> my own config). Do you have it enabled? > >> > > > > Yes, it's enabled. > > > >> > And another round: > >> > > >> > cpufreq stats: OP1:16,78%, OP2:0,24%, OP3:5,14%, OP4:77,83% (72) > >> > > >> > Just once more after doing nothing: > >> > OP1:7,41%, OP2:0,11%, OP3:2,38%, OP4:90,10% (82) > >> > > >> > So I can't agree it's broken. The patch you bisected, actually filtered > >> > out such phenomenon, in which an IRQ made the cpufreq framework > >> > occasionally think we were idling, although we were not. So you got > >> > "bonus" idle time that shouldn't been there in the first place. Now that > >> > the "bonus" idle time is not there, your system load may indeed be so > >> > high that the system never spends 80% or more time in idle? Could that > >> > be the case? Of course, even though I can't agree it's broken, doesn't > >> > mean it isn't somehow broken ;) It'd be nice to get info on other > >> > systems as well... > >> > >> Interestingly, "ondemand" (the governor fixed by the bisected commit) > >> works fine. "conservative" is the only broken one. > >> > > > > If you took timestamps in /arch/x86/kernel/process_**.c: > > (let's assume process_64.c) in cpu_idle() > > around enter_idle(); and __exit_idle(), took the diff, > > added the diffs up, and compared it to system uptime, you could see how > > much time you spend in idle()? I think it's possible that > > even if the cpu load is near 0%, the system may idle only for a bare > > moment (that translates to a buggy pm_idle()), and time is spent > > elsewhere (less than 80% in idle). > > This makes logical sense, but how should I test this? Is there a way > to do this with existing tracers?
Tracers may by themselves add some load into the system.
If I were you, I'd add something like: (I have only one CPU BTW)
static ktime_t time_prior_idle; static int64_t idle_total;
time_prior_idle = ktime_get(); <idle stuff> idle_total += ktime_to_ns(ktime_sub(ktime_get(), time_prior_idle));
and have a sysfs hook (something already present, so you can just cat it) with a trace:
printk("Times: %lld, %lld \n", idle_total, ktime_to_ns(ktime_get()));
Sample output: 374758812519, 386768249832
So I have 386768249832 / 386768249832 = 96.9 % time spent in idle in this case.
(Right, this should provide somewhat descent info, hopefully ;) )
- Eero
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