Re: more on scheduler benchmarks

[Davide Libenzi]

On Monday 22 January 2001 10:30, Mike Kravetz wrote:
> Last week while discussing scheduler benchmarks, Bill Hartner
> made a comment something like the following "the benchmark may
> not even be invoking the scheduler as you expect".  This comment
> did not fully sink in until this weekend when I started thinking
> about changes made to sched_yield() in 2.4.0.  (I'm cc'ing Ingo
> Molnar because I think he was involved in the changes).  If you
> haven't taken a look at sys_sched_yield() in 2.4.0, I suggest
> that you do that now.
>
> A result of new optimizations made to sys_sched_yield() is that
> calling sched_yield() does not result in a 'reschedule' if there
> are no tasks waiting for CPU resources.  Therefore, I would claim
> that running 'scheduler benchmarks' which loop doing sched_yield()
> seem to have little meaning/value for runs where the number of
> looping tasks is less than then number of CPUs in the system.  Is
> that an accurate statement?

With this kind of test tasks are always running.
If You print the nr_running You'll find that this is exactly ( at least ) the 
number of tasks You've spawned so the scheduler is always called.

- Davide