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

[Andrew Morton <akpm@osdl.org>]

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?