Messages in this thread | | | Date | Sat, 18 Nov 2000 21:12:31 +0100 | From | Pavel Machek <> | Subject | Re: rdtsc to mili secs? |
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Hi!
> > > > Intel PIIX-based systems will do duty-cycle throttling, for example. > > > > > > Don't think so. My toshiba is PIIX-based, AFAIC: > > > > Interesting. Some will, definitely. Didn't know that wasn't universal. > > > > Clearly, on a machine like that, there is no hope for RDTSC, at least > > unless the CPU (and OS!) gets notification that the TSC needs to be > > recalibrated whenever it switches. > > > > > Still, it is willing to run with RDTSC at 300MHz, 150MHz, and > > > 40MHz. (The last one in _extreme_ cases when CPU fan fails -- running > > > at 40MHz is better than cooking cpu). > > I believe that pulsing the STPCLK pin of the processor by connecting it > to a say 32kHz signal and then changing the duty cycle of that signal > could have the effect of slowing down the processor to these speeds. > > Somehow I can't believe a PMMX would be able to run at 40MHz. Which in > turn means that STPCLK also stops TSC, which is equally bad.
Why not? From 300MHz to 40MHz... 10 times, that is not that big difference. (I've ran k6/400 at 66MHz, IIRC, while debugging -- I'm not really sure, and don't want to open machine, but it should work).
> Anyway, this should be solvable by checking for clock change in the > timer interrupt. This way we should be able to detect when the clock > went weird with a 10 ms accuracy. And compensate for that. It should be > possible to keep a 'reasonable' clock running even through the clock > changes, where reasonable means constantly growing and as close to real > time as 10 ms difference max. > > Yes, this is not perfect, but still keep every program quite happy and > running.
No. Udelay has just gone wrong and your old ISA xxx card just crashed whole system. Oops.
BTW I mailed patch to do exactly that kind of autodetection to the list some time ago. (I just can't find it now :-( -- search archives for 'TSC is slower than it should be'. Pavel
-- I'm pavel@ucw.cz. "In my country we have almost anarchy and I don't care." Panos Katsaloulis describing me w.r.t. patents at discuss@linmodems.org - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org Please read the FAQ at http://www.tux.org/lkml/
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