Re: [PATCH v0.9.1 3/6] sched/umcg: implement UMCG syscalls

Peter Zijlstra
2021-11-29T22:29:19Z

On Mon, Nov 29, 2021 at 11:07:07PM +0100, Thomas Gleixner wrote:
> On Fri, Nov 26 2021 at 22:52, Peter Zijlstra wrote:

> The size is the same, i.e. 1 bit per nanosecond :)

:-)

> > The only time that's relevant though is when you're going to mix these
> > timestamps with CLOCK_THREAD_CPUTIME_ID, which might just be
> > interesting.
>
> Uuurg. If you want to go towards CLOCK_THREAD_CPUTIME_ID, that's going
> to be really nasty. Actually you can sleep on that clock, but that's a
> completely different universe. If anything like that is desired then we
> need to rewrite that posix CPU timer muck completely with all the bells
> and whistels and race conditions attached to it. *Shudder*

Oh, I wasn't thinking anything as terrible as that. Sleeping on that
clock is fundamentally daft since it doesn't run when thats is
sleeping, consider trying to sleep on your own runtime :-)

I was only considering combining THREAD_CPUTIME timestamps with the
UMCG timestamps to compute how much unmanaged time there was, or other
such things.

Anyway, lets forget I bought this up and assume that for practical
purposes all [ns] are of equal length.