Hi, On 03/10/19 16:36, Waiman Long wrote: > The check_preemption_disabled() function uses cpumask_equal() to see > if the task is bounded to the current CPU only. cpumask_equal() calls > memcmp() to do the comparison. As x86 doesn't have __HAVE_ARCH_MEMCMP, > the slow memcmp() function in lib/string.c is used. > > On a RT kernel that call check_preemption_disabled() very frequently, > below is the perf-record output of a certain microbenchmark: > > 42.75% 2.45% testpmd [kernel.kallsyms] [k] check_preemption_disabled > 40.01% 39.97% testpmd [kernel.kallsyms] [k] memcmp > > We should avoid calling memcmp() in performance critical path. So the > cpumask_equal() call is now replaced with an equivalent simpler check. > > Signed-off-by: Waiman Long <long...@redhat.com> > --- > lib/smp_processor_id.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/lib/smp_processor_id.c b/lib/smp_processor_id.c > index 60ba93fc42ce..bd9571653288 100644 > --- a/lib/smp_processor_id.c > +++ b/lib/smp_processor_id.c > @@ -23,7 +23,7 @@ unsigned int check_preemption_disabled(const char *what1, > const char *what2) > * Kernel threads bound to a single CPU can safely use > * smp_processor_id(): > */ > - if (cpumask_equal(current->cpus_ptr, cpumask_of(this_cpu))) > + if (current->nr_cpus_allowed == 1) > goto out;
Makes sense to me. Reviewed-by: Juri Lelli <juri.le...@redhat.com> Thanks, Juri
