On 10/4/19 5:20 AM, Sebastian Andrzej Siewior wrote: > On 2019-10-03 16:36:08 [-0400], 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. > using a simple integer comparison is still more efficient than what > __HAVE_ARCH_MEMCMP can offer. You are right. My main point is to try to avoid using cpumask_equal() in performance critical path irrespective of this patch. >> Signed-off-by: Waiman Long <long...@redhat.com> > Acked-by: Sebastian Andrzej Siewior <bige...@linutronix.de> > > Sebastian
Cheers, Longman
