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On Thu, 2006-11-09 at 23:38 +0000, Thomas Gleixner wrote: > plain text document attachment > (gtod-mark-tsc-unusable-for-highres-timers.patch) > From: Thomas Gleixner <tglx@linutronix.de> > The TSC is too unstable and unreliable to be used with high resolution timers. > The automatic detection of TSC unstability fails once we switched to high > resolution mode, because the tick emulation would use the TSC as reference. > This results in a circular dependency. Mark it unusable for high res upfront. > > [akpm@osdl.org: updated for i386-time-avoid-pit-smp-lockups.patch] > Signed-off-by: Thomas Gleixner <tglx@linutronix.de> > Signed-off-by: Ingo Molnar <mingo@elte.hu> > > diff -puN arch/i386/kernel/tsc.c~gtod-mark-tsc-unusable-for-highres-timers arch/i386/kernel/tsc.c > --- a/arch/i386/kernel/tsc.c~gtod-mark-tsc-unusable-for-highres-timers > +++ a/arch/i386/kernel/tsc.c > @@ -459,10 +459,23 @@ static int __init init_tsc_clocksource(v > current_tsc_khz = tsc_khz; > clocksource_tsc.mult = clocksource_khz2mult(current_tsc_khz, > clocksource_tsc.shift); > +#ifndef CONFIG_HIGH_RES_TIMERS > /* lower the rating if we already know its unstable: */ > if (check_tsc_unstable()) > clocksource_tsc.rating = 0; > - > +#else > + /* > + * Mark TSC unsuitable for high resolution timers. TSC has so > + * many pitfalls: frequency changes, stop in idle ... When we > + * switch to high resolution mode we can not longer detect a > + * firmware caused frequency change, as the emulated tick uses > + * TSC as reference. This results in a circular dependency. > + * Switch only to high resolution mode, if pm_timer or such > + * is available. > + */ > + clocksource_tsc.rating = 50; > + clocksource_tsc.is_continuous = 0; > +#endif > init_timer(&verify_tsc_freq_timer); > verify_tsc_freq_timer.function = verify_tsc_freq; > verify_tsc_freq_timer.expires = Hmmm. I wish this patch was unnecessary, but I don't see an easy solution. Mind adding a warning so users know why a system that might use the TSC normally does not use the TSC w/ highres timers? Otherwise looks ok. Acked-by: John Stultz <johnstul@us.ibm.com> thanks -john - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@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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