[U-Boot] [RFC][Timer API] Revised Specification - Implementation details

[Wolfgang Denk]

Dear Graeme Russ,

In message <4DE383D3.7020008 at gmail.com> you wrote:
> 
> Some platforms are _way_ worse than this - I am sure I have seen a udelay()
> done with the millisecond time - So udelay(100) could be closer to
> udelay(1000) - So your above 5 second delay could take as long as 50 seconds!!!

That should show up quickly as soon as you run a "sleep 5" command on
the console (which is implemented like that).

> > 	while (test_for_event() == 0) {
> > 		now = get_timer(0);
> > 		if ((now - start) > timeout)
> > 			handle_timeout();
> > 
> > 		udelay(100);
> > 	}
> > 
> >    Here the loop overhead caused by short delay which may result in a
> >    high number of calls to test_for_event() gets eliminated because
> >    the time reference is independet of the delay.
> 
> I personally think _any_ timeout greater than 1s (maybe even >500ms) should
> be done this way

Agreed. As soon as the timeout is >> the interval size of the
underlying timer service this is the best we can do.

> > 	start = get_timer(0);
> > 
> > 	do_something_complicated();
> > 
> > 	now = get_timer(0);
> > 
> > 	printf("execution time: %ld millisec\n", now - start);
> 
> Currently fails spectacularly if do_something_complicated() involves a
> delay loop which calls reset_timer()

Note that I (intentionally) always used argument 0 in the calls to
get_timer().  I think we really should get rid of this argument.

> I think this may become more popular for performance tuning once the API
> has been established. The desire for boot profiling was what initially made
> me investigate the API given the current use of reset_timer() prohibits
> profiling across a timeout loop.

Agreed.

Best regards,

Wolfgang Denk

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