Re: [PATCH 39/49] arch/s390: replace cpumask_weight with cpumask_weight_eq where appropriate

[Yury Norov]

On Fri, Feb 11, 2022 at 07:54:26AM +0100, Sven Schnelle wrote:
> Hi Yury,
> 
> Yury Norov <yury.norov@xxxxxxxxx> writes:
> 
> > cfset_all_start() calls cpumask_weight() to compare the weight of cpumask
> > with a given number. We can do it more efficiently with
> > cpumask_weight_{eq, ...} because conditional cpumask_weight may stop
> > traversing the cpumask earlier, as soon as condition is (or can't be) met.
> >
> > Signed-off-by: Yury Norov <yury.norov@xxxxxxxxx>
> > ---
> >  arch/s390/kernel/perf_cpum_cf.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/s390/kernel/perf_cpum_cf.c b/arch/s390/kernel/perf_cpum_cf.c
> > index ee8707abdb6a..4d217f7f5ccf 100644
> > --- a/arch/s390/kernel/perf_cpum_cf.c
> > +++ b/arch/s390/kernel/perf_cpum_cf.c
> > @@ -975,7 +975,7 @@ static int cfset_all_start(struct cfset_request *req)
> >  		return -ENOMEM;
> >  	cpumask_and(mask, &req->mask, cpu_online_mask);
> >  	on_each_cpu_mask(mask, cfset_ioctl_on, &p, 1);
> > -	if (atomic_read(&p.cpus_ack) != cpumask_weight(mask)) {
> > +	if (!cpumask_weight_eq(mask, atomic_read(&p.cpus_ack))) {
> >  		on_each_cpu_mask(mask, cfset_ioctl_off, &p, 1);
> >  		rc = -EIO;
> >  		debug_sprintf_event(cf_dbg, 4, "%s CPUs missing", __func__);
> 
> given that you're adding a bunch of these functions - gt,lt,eq and
> others, i wonder whether it makes sense to also add cpumask_weight_ne(),
> so one could just write:
> 
> if (cpumask_weight_ne(mask, atomic_read(&p.cpus_ack))) {
> 	...
> }
> 
> ?

It will have 3 users in cpumask + 1 in nodemask. I have no strong opinion
whether we need it or not. Let's see what people say.

Thanks,
Yury