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SubjectRe: [patch] recover lost ticks

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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