Re: Scheduling tests on IPC methods, fc6, sd0.48, cfs12

Bill Davidsen
2007-05-22T22:21:31Z

Ingo Molnar wrote:
> * Bill Davidsen <davidsen@tmr.com> wrote:
>
>> I have posted the results of my initial testing, measuring IPC rates
>> using various schedulers under no load, limited nice load, and heavy
>> load at nice 0.
>>
>> http://www.tmr.com/~davidsen/ctxbench_testing.html
>
> nice! For this to become really representative though i'd like to ask
> for a real workload function to be used after the task gets the
> lock/message. The reason is that there is an inherent balancing conflict
> in this area: should the scheduler 'spread' tasks to other CPUs or not?
> In general, for all workloads that matter, the answer is almost always:
> 'yes, it should'.
>
Added to the short to-do list. Note that this was originally simply a
check to see which IPC works best (or at all) in an o/s. It has been
useful for some other things, and an option for work will be forthcoming.

> But in your ctxbench results the work a task performs after doing IPC is
> not reflected (the benchmark goes about to do the next IPC - hence
> penalizing scheduling strategies that move tasks to other CPUs) - hence
> the bonus of a scheduler properly spreading out tasks is not measured
> fairly. A real-life IPC workload is rarely just about messaging around
> (a single task could do that itself) - some real workload function is
> used. You can see this effect yourself: do a "taskset -p 01 $$" before
> running ctxbench and you'll see the numbers improve significantly on all
> of the schedulers.
>
> As a solution i'd suggest to add a workload function with a 100 or 200
> usecs (or larger) cost (as a fixed-length loop or something like that)
> so that the 'spreading' effect/benefit gets measured fairly too.
>
Can do.

--
Bill Davidsen <davidsen@tmr.com>
"We have more to fear from the bungling of the incompetent than from
the machinations of the wicked." - from Slashdot