[Python-Dev] Drop the new time.wallclock() function?

[Christian Tismer]

The performancecounter is a thing that typically gets intercepted by
the VM infrastructure and does no longer work as a reliable timing
source. In PyPy there are tests which check certain assumptions
how much the performancecounter must advance at least between
a few opcodes, and that does not work in a VM.

cheers - Chris

On 3/13/12 6:11 PM, Kristján Valur Jónsson wrote:
> Interesting thought.
> Althougn I don't see how that could fail on windows, if the QPC function is really just talking to a clock chip, surely that hasn't been virtualized.
> Is there an actual example of windows hardware where this api fails (virtual or not?)  Perhaps there is no real need to have a fallback mechanism, and it would even be best to write such a mechanism inside the function itself, and just return getsystemtimeasfiletime() instead.
>
> K
>
> -----Original Message-----
> From: Christian Tismer [mailto:tismer at stackless.com]
> Sent: 13. mars 2012 18:07
> To: Kristján Valur Jónsson
> Cc: Guido van Rossum; Victor Stinner; Python Dev
> Subject: Re: [Python-Dev] Drop the new time.wallclock() function?
>
> Btw., have you considered virtual machines?
> I happen to run windows in Parallels or Virtualbox quite often.
> There the "wall clock" stuff notoriously does not work.
>
> It would be good (but difficult?) if the supposed-to-be-accurate clock could test itself, if it works at all, and replace itself with a fallback.
>
> In my case, this causes quite a few PyPy tests to fail ;-)
>
> ciao -- Chris
>


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