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SubjectRe: [patch] recover lost ticks
Under 2.0.3x, if you run with a serial console, then you will find that printk's

have interrupts disabled while they run. Thus a 100character printk takes
about 100ms (10 ticks lost) on a 9600 bps line.

I don't know whether this is fixed in 2.2, but if not, then the lost tick
detector ought to fill in the lost ticks rather than just complain about them.

Philip

Ingo Molnar wrote:

> On Mon, 15 Mar 1999, Andrea Arcangeli wrote:
>
> > If the tsc goes as hell gettimeofday will die too, and the TSC is
> > explicity declared from Intel as a really safely trustable thing, so if
> > the TSC will die I expect many other part of the CPU to die too.
>
> (i only pointed out that TSC bugs/inconsistencies (which happened in the
> past) now might have yet another side-effect. [there was a robustness
> claim])
>
> > And maybe somebody may really intentionally take the cpu clied for more
> > than 10msec for some strange usage.
>
> (do you know about any such legitimate use. I've used such things myself
> in the APIC code, it's not legitimate and i've fixed it.)
>
> > Since we'll printk a message anyway and so we have just increased the
> > complexity of the code anyway, so why not to also recover the lost tick in
> > a slow path as I do?
>
> (You have added 30 lines of code, i've removed 20. Thats a 50 lines
> difference.)
>
> > >maintain piece of code to 'fix' the symptom of a fundamentally broken and
> > >rare case, instead of just detecting and fixing the real reason.
> >
> > I am not fixing the symptom, I am recovering the bug at runtime kprinting
> > the useful information as in your patch but with the difference that then
> > I am allowing the machine to run fine until the problem will get fixed
> > (and to get it fixed you may need to wait some time like in the scsi
> > code).
>
> the SCSI case is pure paranoia and an unmaintained subsystem. Fixing (one
> of ) the effects of overlong cli() just delays the real fix. (why should
> we bother fixing them when system time runs just fine) Some other
> side-effects of overlong clis, apart from lost timer ticks: lost
> characters on the serial line, lost keyboard events. If someone doing
> strange things can live with these other effects, he sure can live with
> lost timer ticks as well.
>
> -- mingo
>
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--
---
Philip Gladstone (working at home)
Raptor Systems, A division of Axent Technologies



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