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    SubjectRe: [PATCH 07/16] smp: optimize smp_call_function_many_cond()
    On Mon, Jul 18, 2022 at 12:28:35PM -0700, Yury Norov wrote:

    > diff --git a/kernel/smp.c b/kernel/smp.c
    > index dd215f439426..7ed2b9b12f74 100644
    > --- a/kernel/smp.c
    > +++ b/kernel/smp.c
    > @@ -880,6 +880,28 @@ EXPORT_SYMBOL_GPL(smp_call_function_any);
    > #define SCF_WAIT (1U << 0)
    > #define SCF_RUN_LOCAL (1U << 1)
    >
    > +/* Check if we need remote execution, i.e., any CPU excluding this one. */
    > +static inline bool __need_remote_exec(const struct cpumask *mask, unsigned int this_cpu)
    > +{
    > + unsigned int cpu;
    > +
    > + switch (num_online_cpus()) {
    > + case 0:
    > + return false;
    > + case 1:
    > + return cpu_online(this_cpu) ? false : true;
    > + default:
    > + if (mask == cpu_online_mask)
    > + return true;
    > + }
    > +
    > + cpu = cpumask_first_and(mask, cpu_online_mask);
    > + if (cpu == this_cpu)
    > + cpu = cpumask_next_and(cpu, mask, cpu_online_mask);
    > +
    > + return cpu < nr_cpu_ids;
    > +}
    > +
    > static void smp_call_function_many_cond(const struct cpumask *mask,
    > smp_call_func_t func, void *info,
    > unsigned int scf_flags,
    > @@ -916,12 +938,7 @@ static void smp_call_function_many_cond(const struct cpumask *mask,
    > if ((scf_flags & SCF_RUN_LOCAL) && cpumask_test_cpu(this_cpu, mask))
    > run_local = true;
    >
    > - /* Check if we need remote execution, i.e., any CPU excluding this one. */
    > - cpu = cpumask_first_and(mask, cpu_online_mask);
    > - if (cpu == this_cpu)
    > - cpu = cpumask_next_and(cpu, mask, cpu_online_mask);
    > - if (cpu < nr_cpu_ids)
    > - run_remote = true;
    > + run_remote = __need_remote_exec(mask, this_cpu);
    >
    > if (run_remote) {
    > cfd = this_cpu_ptr(&cfd_data);

    This is more complex code for, very little to no gain. Why ?!

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