Re: [PATCH 2.6.13-rc5-gitNOW] msleep() cannot be used from interrupt

Andrew Morton
2005-08-05T18:59:44Z

Petr Vandrovec <vandrove@vc.cvut.cz> wrote:
>
> Since beginning of July my Opteron box was randomly crashing and being rebooted
> by hardware watchdog. Today it finally did it in front of me, and this patch
> will hopefully fix it.
>
> Problem is that at the end of June (28th, commit
> 47f176fdaf8924bc83fddcf9658f2fd3ef60d573, [PATCH] Using msleep() instead of HZ)
> rtc_get_rtc_time was converted to use msleep() instead of busy waiting. But
> rtc_get_rtc_time is used by hpet_rtc_interrupt, and scheduling is not allowed
> during interrupt. So I'm reverting this part of original change, replacing
> msleep() back with busy loop.
>
> Original old code was busy waiting for 20ms, while on my hardware in the worst
> case update-in-progress bit was asserted for at most 363 passes through loop
> (on 2GHz dual Opteron), much less than even one jiffie, not even talking
> about 20ms. So I changed code to just wait only as long as necessary. Otherwise
> when RTC was set to generate 8192Hz timer, it stopped doing anything for
> 20ms (160 pulses were skipped!) from time to time, and this is rather suboptimal
> as far as I can tell.

That's all pretty sad stuff. I guess for now we can go back to the busy
loop. Longer-term it would be nice if we could tune up the HPET driver in
some manner so we can avoid this busy-wait-in-interrupt.

I'm not sure who the HPET maintainer/expert is nowadays. Robert Picco did
the original work but I haven't seen Robert around for a long time?