[PATCH] 2.3.41 scheduler change

[Jamie Lokier]

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...

> 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.

have a nice day,
-- Jamie

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