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authorWaiman Long <longman@redhat.com>2019-10-03 16:36:08 -0400
committerIngo Molnar <mingo@kernel.org>2019-10-09 12:46:10 +0200
commite950cca3f3c40902a052a78a36b3fac1f8a62d19 (patch)
tree961c8e7e85d67cdbcc4fe8b367d88d552ec317b8
parente3280b54afed870d531571212f1fc375df39b7d2 (diff)
lib/smp_processor_id: Don't use cpumask_equal()
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@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Juri Lelli <juri.lelli@redhat.com> Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Masami Hiramatsu <mhiramat@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Link: https://lkml.kernel.org/r/20191003203608.21881-1-longman@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
-rw-r--r--lib/smp_processor_id.c2
1 files changed, 1 insertions, 1 deletions
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;
/*