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. > Signed-off-by: Waiman Long <long...@redhat.com> Acked-by: Sebastian Andrzej Siewior <bige...@linutronix.de> Sebastian
