4.19.94-rt39-rc2 stable review patch. If anyone has any objections, please let me know. ------------------ From: Waiman Long <longman@xxxxxxxxxx> [ Upstream commit 659252061477862f45b79e1de169e6030f5c8918 ] 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 <longman@xxxxxxxxxx> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx> --- 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 fb35c45b9421..b8a8a8db2d75 100644 --- a/lib/smp_processor_id.c +++ b/lib/smp_processor_id.c @@ -22,7 +22,7 @@ notrace static unsigned int check_preemption_disabled(const char *what1, * 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; /* -- 2.24.1
