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SubjectRe: [PATCH] sched.c
Lahti Oy wrote:
>
> Small patch that makes NR_CPUS loops decrement from 31 to 0 in sched.c to
> squeeze out some cycles (of course only on SMP machines). Also deprecated a
> macro that was only used once in the code and changed one if-conditional to
> else if.
>
> ...
>
> - for (i = 0; i < NR_CPUS; i++)
> + for (i = NR_CPUS; i; i--)
> sum += cpu_rq(i)->nr_running;

Off-by-one there. You'd want

for (i = NR_CPUS; --i >= 0; )

or something similarly foul ;)

But these are not performance-critical functions. And by far the
most inefficient part of them is that they're reading data for
CPUs which cannot exist. That can be fixed with a `cpu_possible(i)'
test in there, but Rusty was going to give us a `for_each_cpu' macro.
We haven't seen that yet.
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