[PATCH] 2.3.41 scheduler change

[Rik van Riel]

On Sun, 30 Jan 2000, Jamie Lokier wrote:
> Rik van Riel wrote:
> > > Are you sure that CPU measurement is real?  These sort of changes
> > > tend to break process accounting.
> > 
> > I agree that process accounting is kind of random.
> > However, it is exactly this randomness that makes
> > me believe that it really isn't a measurement fault.
> 
> With your changes, I wouldn't be surprised to find an entirely
> non-random measurement error.  You're messing with scheduling
> quanta, and thats exactly where measurement tends to misrepresent
> what's going on.  But...

I'm not at all measuring with scheduling quanta. All my patch
changes is _when_ tasks get scheduled, not how much time they
get.

> > Before the patch, xmms cpu usage varied between 70
> > and 95%. Now it varies between 50 and 75%, this
> > looks like too big a thing to be random.
> 
> One way to test this directly is to run a second process at the
> same time that does:
> 
>   while (1) {
>     i = 0;
>     time = read_tsc ();
>     while (read_tsc () - time < 1 second)
>       i++;
>     printf( "%d loops per second\n", i );
>   }
> 
> The inner loop should be written to use as little cache footprint
> as possible of course.
> 
> If your patch really works, then xmms will use less CPU and this
> will get more cycles.

Indeed. Maybe I'll try this when I'm fully awake again
(feeling very tired now)...

cheers,

Rik
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