RE: [PATCH 43/54] drivers/hv: replace cpumask_weight with cpumask_weight_eq

[Vitaly Kuznetsov <vkuznets@redhat.com>]

"Michael Kelley (LINUX)" <mikelley@microsoft.com> writes:

> From: Vitaly Kuznetsov <vkuznets@redhat.com> Sent: Monday, January 24, 2022 1:20 AM
>> 
>> Yury Norov <yury.norov@gmail.com> writes:
>> 
...
>> >
>> > diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
>> > index 60375879612f..7420a5fd47b5 100644
>> > --- a/drivers/hv/channel_mgmt.c
>> > +++ b/drivers/hv/channel_mgmt.c
>> > @@ -762,8 +762,8 @@ static void init_vp_index(struct vmbus_channel *channel)
>> >  		}
>> >  		alloced_mask = &hv_context.hv_numa_map[numa_node];
>> >
>> > -		if (cpumask_weight(alloced_mask) ==
>> > -		    cpumask_weight(cpumask_of_node(numa_node))) {
>> > +		if (cpumask_weight_eq(alloced_mask,
>> > +			    cpumask_weight(cpumask_of_node(numa_node)))) {
>> 
>> This code is not performace critical and I prefer the old version:
>> 
>>  	cpumask_weight() == cpumask_weight()
>> 
>>  looks better than
>> 
>> 	cpumask_weight_eq(..., cpumask_weight())
>> 
>> (let alone the inner cpumask_of_node()) to me.
>> 
>> >  			/*
>> >  			 * We have cycled through all the CPUs in the node;
>> >  			 * reset the alloced map.
>> 
> I agree with Vitaly in preferring the old version, and indeed performance
> here is a shrug.  But actually, I think the old version is a poorly coded way
> to determine if the two cpumasks are equal. The following would correctly
> capture the intent:
>
> 	if (cpumask_equal(alloced_mask, cpumask_of_node(numa_node))
>

Indeed. While it seems that only CPUs from 'cpumask_of_node(numa_node)'
can be set in 'alloced_mask' (and thus the comparison is valid), there's
no real need to weigh anything. I'll send a patch.

-- 
Vitaly