Re: [patch 17/17] Add a sched_clock paravirt_op

[Andi Kleen <ak@suse.de>]

On Monday 02 April 2007 08:47, Jeremy Fitzhardinge wrote:
> Andi Kleen wrote:
> > I think it would be much cleaner if you didn't implement your own sched_clock,
> > but you adjust ns_base/last_tsc to account for your lost cycles.
> > This could be done cleanly by adding a new function to sched-clock.c
> > Possibly such a function could be used by other parts of the kernel
> > in the future too.
> >   
> 
> Cleaner how?  This seems pretty to me.  Xen can return a
> clock measuring unstolen nanoseconds, 

Do you also get a clock for stolen nanoseconds? 

> which maps directly to the 
> sched_clock interface, doesn't need any of the existing sched_clock
> code.  I suppose I could map the Xen interface onto some abstract
> "cycles" notion and hook it into the tsc machinery, but it seems like it
> would be a forced fit.  In general, my approach has been to choose the
> higher-level interface over a lower-level one, all other things being equal.

No need for cycles, you could just subtract the stolen ns if you
can get those.

-Andi