Re: [PATCH v2 3/5] change number_of_cpusets to an atomic

On Tue, 24 Apr 2012, Glauber Costa wrote:

quoted

Would this not also be a good case to introduce static branching?

number_of_cpusets is used to avoid going through unnecessary processing
should there be no cpusets in use.

static branches comes with a set of problems themselves, so I usually prefer
to use them only in places where we don't want to pay even a cache miss if we
can avoid, or a function call, or anything like that - like the slub cache
alloc as you may have seen in my kmem memcg series.

It doesn't seem to be the case here.

How did you figure that? number_of_cpusets was introduced exactly because
the functions are used in places where we do not pay the cost of calling
__cpuset_node_allowed_soft/hardwall. Have a look at these. They may take
locks etc etc in critical allocation paths