On 10/3/19 4:18 PM, 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 check that > makes no external function call. > > Signed-off-by: Waiman Long <[email protected]> > --- > lib/smp_processor_id.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/lib/smp_processor_id.c b/lib/smp_processor_id.c > index 60ba93fc42ce..3fee05ac92f8 100644 > --- a/lib/smp_processor_id.c > +++ b/lib/smp_processor_id.c > @@ -23,7 +23,8 @@ 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) && > + cpumask_test_cpu(this_cpu, current->cpus_ptr)) > goto out; > > /*
My bad. The second check isn't really necessary. Cheers, Longman
