Fix nanosleep returning negative rem

[David Allsopp]

Corinna Vinschen wrote:
> Sent: 21 July 2021 10:33
> To: cygwin-patches@cygwin.com
> Subject: Re: Fix nanosleep returning negative rem
> 
> On Jul 21 11:30, Corinna Vinschen wrote:
> > I wrote a quick STC using the NT API calls and I can't reproduce the
> > problem with this code either.  The output is either
> >
> >   SignalState: 1 TimeRemaining: -5354077459183
> >
> > or
> >
> >   SignalState: 0 TimeRemaining: 653
> >
> > I never get a small negative value in the latter case.  Can you
> > reproduce your problem with this testcase or tweak it to reproduce it?
> 
> Now I actually attached the code :}

:) Yes, I can reproduce - I didn't even need a loop! Third time:

  dra@Thor /cygdrive/c/Scratch/nanosleep
  $ ./timer
  SignalState: 0 TimeRemaining: -1151

That said, I can get it easily get this on my desktop (AMD Ryzen Threadripper 3990X) but not at all on my laptop (Intel Core i7-8650U). On the laptop, ignoring the couple of signalled cases, 747 runs of timer.c give values between 131597-149947 with a very narrow SD (~4000) whereas on the AMD chip, 738 runs gives a range of -2722 to 149896 with a relatively wider SD of ~23000.

The CI system where this was first seen is an virtualised Intel system so it doesn't appear to be as simple as CPU manufacturer or even core count. That said, I'm not at all familiar with the details of how this works, but I expect the timer for these things is part of the chipset, not the CPU?!

Best,


D