On Mon, Jan 21, 2013 at 02:38:44PM +0800, Feng Tang wrote: > Date: Mon, 21 Jan 2013 14:38:44 +0800 > From: Feng Tang <feng.t...@intel.com> > To: Thomas Gleixner <t...@linutronix.de>, John Stultz > <john.stu...@linaro.org>, Ingo Molnar <mi...@elte.hu>, "H. Peter Anvin" > <h...@linux.intel.com>, x...@kernel.org, Len Brown <l...@kernel.org>, > "Rafael J. Wysocki" <rafael.j.wyso...@intel.com>, > linux-kernel@vger.kernel.org > Cc: Feng Tang <feng.t...@intel.com> > Subject: [RFC PATCH 4/5] clocksource: Enlarge the maxim time interval when > configuring the scale and shift > X-Mailer: git-send-email 1.7.9.5 > > On our x86 platform, we see a failure case of calling clocksource_cyc2ns(), > which return a negative value. The reason is the time interval was large > (more than 1000 seconds), while its TSC frequency is 2GHz, so the following > fomular overflowed: > ((u64) cycles * mult) >> shift > > So enlarge the time interval from 10 mins to 40 mins to fix the bug. > > Another solution may be adding a "max_interval" in struct clocksource, and > use a default value (like current 10 minutes) when clocksource driver > doesn't set it. > As you said, it looks like it is a littleb it arbitrary from 10m -> 40m, I think max_interval is a better choice, if timer guys not minding too many control knobs :-).
> Signed-off-by: Feng Tang <feng.t...@intel.com> > --- > kernel/time/clocksource.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c > index c958338..48fbfcb 100644 > --- a/kernel/time/clocksource.c > +++ b/kernel/time/clocksource.c > @@ -663,7 +663,7 @@ void __clocksource_updatefreq_scale(struct clocksource > *cs, u32 scale, u32 freq) > * Calc the maximum number of seconds which we can run before > * wrapping around. For clocksources which have a mask > 32bit > * we need to limit the max sleep time to have a good > - * conversion precision. 10 minutes is still a reasonable > + * conversion precision. 40 minutes is still a reasonable > * amount. That results in a shift value of 24 for a > * clocksource with mask >= 40bit and f >= 4GHz. That maps to > * ~ 0.06ppm granularity for NTP. We apply the same 12.5% > @@ -674,8 +674,8 @@ void __clocksource_updatefreq_scale(struct clocksource > *cs, u32 scale, u32 freq) > do_div(sec, scale); > if (!sec) > sec = 1; > - else if (sec > 600 && cs->mask > UINT_MAX) > - sec = 600; > + else if (sec > 2400 && cs->mask > UINT_MAX) > + sec = 2400; > > clocks_calc_mult_shift(&cs->mult, &cs->shift, freq, > NSEC_PER_SEC / scale, sec * scale); > -- > 1.7.9.5 > > -- > 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/
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