On Sun, Jan 11, 2015 at 3:47 AM, Richard Cochran <richardcoch...@gmail.com> wrote: > > This series added: > > + /* Return 50% of the actual maximum, so we can detect bad values */ > + max_nsecs >>= 1; > > and then... > > On Fri, Jan 09, 2015 at 04:34:21PM -0800, John Stultz wrote: >> @@ -760,7 +746,8 @@ void __clocksource_updatefreq_scale(struct clocksource >> *cs, u32 scale, u32 freq) >> cs->maxadj = clocksource_max_adjustment(cs); >> } >> >> - cs->max_idle_ns = clocksource_max_deferment(cs); >> + cs->max_idle_ns = clocks_calc_max_nsecs(cs->mult, cs->shift, >> + cs->maxadj, cs->mask); >> } >> EXPORT_SYMBOL_GPL(__clocksource_updatefreq_scale); >> >> @@ -807,7 +794,8 @@ int clocksource_register(struct clocksource *cs) >> cs->name); >> >> /* calculate max idle time permitted for this clocksource */ >> - cs->max_idle_ns = clocksource_max_deferment(cs); >> + cs->max_idle_ns = clocks_calc_max_nsecs(cs->mult, cs->shift, >> + cs->maxadj, cs->mask); > > ... the whole world's maximum idle time is artificially reduced by > half in order to catch some rare HW bug? Not a very green solution.
So, the first patch had a cleanup which removed case where the max mult value was being calculated assuming nanoseconds was a s64 instead of a u64, which resulted in the max_idle_ns to be halved. So this doesn't actually cost us more over what the current kernel does. In fact, the cleanup removed the extra 12.5% reductions that were applied, so for the HPET in qemu on my system, the max idle goes from ~16 secs to ~21 secs with this patchset (if I'm remembering correctly). But I'm open to put this under a debug config if its justified (part of Linus' concern w/ clocksource code is that its had a few spots that were needlessly complex, so some weighing of performance/power vs simplified logic should be done). Do you have a specific case in mind that you're worried about? thanks -john -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
