Re: [PATCH v3 0/3] perf: User/kernel time correlation and event generation

[Richard Cochran <richardcochran-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On Tue, Nov 04, 2014 at 09:01:31AM +0100, Arnd Bergmann wrote:
> On Monday 03 November 2014 17:11:53 John Stultz wrote:
> > I've got some thoughts on what a possible interface that wouldn't be
> > awful could look like, but I'm still hesitant because I don't really
> > know if exposing this sort of data is actually a good idea long term.
>  
> I was also thinking (while working on an unrelated patch) we could use
> a system call like
> 
> int clock_getoffset(clockid_t clkid, struct timespec *offs);
> 
> that returns the current offset between CLOCK_REALTIME and the
> requested timebase. It is of course racy, but so is every use
> of CLOCK_REALTIME. We could also use a reference other than
> CLOCK_REALTIME that might be more stable, but passing two arbitrary
> clocks as input would make this much more complex to implement.

No, it is really easy to implement. Just drop the idea of "atomic". It
really is not necessary or even possible.

Thanks,
Richard