Re: [PATCH v2 3/3] sched/fair: Add compile time check in fastpaths for CONFIG_SCHED_SMT=n

[Shrikanth Hegde <sshegde@linux.ibm.com>]

Hi Prateek.

> ... I think the if() above can simply check for sched_smt_active()
> before calling is_core_idle() like:
> 
>      if (sched_smt_active() &&
>          !(env->sd->flags & SD_SHARE_CPUCAPACITY) &&
>          !is_core_idle(cpu)) {
>          ...
>      }
> 
> That way, we ensure we don't call is_core_idle() and the cpumask_and()
> unnecessarily on topologies that don't have SMT domain similar to how
> sched_use_asym_prio() guards the call to is_core_idle().
> 
> Thoughts?
> 
In addition, Do you think it makes sense to consolidate use of
sched_smt_present always using sched_smt_active() ?


static __always_inline bool sched_smt_active(void)
{
         return static_branch_likely(&sched_smt_present);
}

kernel/sched/core_sched.c:      if (!static_branch_likely(&sched_smt_present))
kernel/sched/fair.c:    if (!static_branch_likely(&sched_smt_present) ||
kernel/sched/sched.h:   if (static_branch_unlikely(&sched_smt_present))


The last being differing with unlikely in update_idle_core.
Does it make sense to call sched_smt_active there as well?