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| author | Waiman Long <longman@redhat.com> | 2019-10-03 16:36:08 -0400 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2019-10-09 12:46:10 +0200 |
| commit | e950cca3f3c40902a052a78a36b3fac1f8a62d19 (patch) | |
| tree | 961c8e7e85d67cdbcc4fe8b367d88d552ec317b8 | |
| parent | e3280b54afed870d531571212f1fc375df39b7d2 (diff) | |
| download | lwn-e950cca3f3c40902a052a78a36b3fac1f8a62d19.tar.gz lwn-e950cca3f3c40902a052a78a36b3fac1f8a62d19.zip | |
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.c | 2 |
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; /* |