Re: [PATCH] N1int for interactivity

[Mike Galbraith <efault@gmx.de>]

At 02:03 PM 7/15/2003 +1000, Con Kolivas wrote:
>On Tue, 15 Jul 2003 13:59, Andrew Morton wrote:
> > Con Kolivas <kernel@kolivas.org> wrote:
> > > I've modified Mike Galbraith's nanosleep work for greater resolution to
> > > help the interactivity estimator work I've done in the O*int patches.

(I think a repeat of an earlier public warning wrt this diff may be in 
order: run irman/contest before you proceed... here there be giant economy 
sized dragons)

> > >
> > > +inline void __scheduler_tick(runqueue_t *rq, task_t *p)
> >
> > Two callsites, this guy shouldn't be inlined.

(I just wild-guessed that it'd be a tiny bit faster while i was coding... 
_the_ fast-path and all)

> >
> > Should it have static scope?  The code as-is generates a third copy...
> >
> > >  static unsigned long long monotonic_clock_tsc(void)
> > >  {
> > >     unsigned long long last_offset, this_offset, base;
> > > -
> > > +   unsigned long flags;
> > > +
> > >     /* atomically read monotonic base & last_offset */
> > > -   read_lock_irq(&monotonic_lock);
> > > +   read_lock_irqsave(&monotonic_lock, flags);
> > >     last_offset = ((unsigned long long)last_tsc_high<<32)|last_tsc_low;
> > >     base = monotonic_base;
> > > -   read_unlock_irq(&monotonic_lock);
> > > +   read_unlock_irqrestore(&monotonic_lock, flags);
> > >
> > >     /* Read the Time Stamp Counter */
> >
> > Why do we need to take a global lock here?  Can't we use
> > get_cycles() or something?

The scalability issue is gone I'm told.

 > Have all the other architectures been reviewed to see if they need this
> > change?
>
>I'm calling for help here. This is getting way out of my depth; I've simply
>applied Mike's patch.

Everyone will likely need that, or there will be major explosions.  You'll 
also have to deal with the no-tsc case... either return jiffies * 1000000 
or make it a config option.

(I'd go with a config option if I were you...dragons aren't all that likely 
to torch a desktop load, but if you do this globally, I'm quite certain 
that something is going to get char-broiled;)

         -Mike