Re: [PATCH] CFS: Fix missing digit off in wmult table

[Ingo Molnar <mingo@elte.hu>]

* James Bruce <bruce@andrew.cmu.edu> wrote:

> While we're at it, isn't the comment above the wmult table incorrect? 
> The multiplier is 1.25, meaning a 25% change per nice level, not 10%.

yes, the weight multiplier 1.25, but the actual difference in CPU 
utilization, when running two CPU intense tasks, is ~10%:

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
 8246 mingo     20   0  1576  244  196 R   55  0.0   0:11.96 loop
 8247 mingo     21   1  1576  244  196 R   45  0.0   0:10.52 loop

so the first task 'wins' +10% CPU utilization (relative to the 50% it 
had before), the second task 'loses' -10% CPU utilization (relative to 
the 50% it had before).

so what the comment says is true:

 * The "10% effect" is relative and cumulative: from _any_ nice level,
 * if you go up 1 level, it's -10% CPU usage, if you go down 1 level
 * it's +10% CPU usage.

for there to be a ~+10% change in CPU utilization for a task that races 
against another CPU-intense task there needs to be a ~25% change in the 
weight.

	Ingo
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/