Re: [PATCH 3/3] sched/nohz: Remove weird error handling from find_new_ilb()

[Valentin Schneider]

On 06/10/23 13:01, Ingo Molnar wrote:
> * Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
>> On Fri, Oct 06, 2023 at 12:25:18PM +0200, Ingo Molnar wrote:
>> > find_new_ilb() returns nr_cpu_ids on failure - which is a weird
>> > choice in itself: not only is it a global variable, it is
>> > a +1 out of bounds CPU index...
>> 
>> FWIW this is what all the cpumask bitops return when they've exhausted
>> the mask. Eg. no bits left set etc..
>
> yeah, which then results in type-forcing uglies like:
>
>    kernel/events/core.c:	if ((unsigned)cpu >= nr_cpu_ids) {
>    kernel/events/core.c:   if ((unsigned)cpu >= nr_cpu_ids) {
>    kernel/smp.c:	   if ((unsigned)cpu >= nr_cpu_ids || !cpu_online(cpu)) {

I can't see why we'd want smp_call_function_single*() /
generic_exec_single() to take a signed int as input, shouldn't this just be
unsigned?

The perf thing does look like it wants signed though...

>
> :-/
>
> So I don't think this is a particularly well thought-out interface.
>
> Thanks,
>
> 	Ingo