diff options
Diffstat (limited to 'debian/patches-rt/0301-lib-smp_processor_id-Don-t-use-cpumask_equal.patch')
| -rw-r--r-- | debian/patches-rt/0301-lib-smp_processor_id-Don-t-use-cpumask_equal.patch | 41 |
1 files changed, 41 insertions, 0 deletions
diff --git a/debian/patches-rt/0301-lib-smp_processor_id-Don-t-use-cpumask_equal.patch b/debian/patches-rt/0301-lib-smp_processor_id-Don-t-use-cpumask_equal.patch new file mode 100644 index 000000000..456e9caae --- /dev/null +++ b/debian/patches-rt/0301-lib-smp_processor_id-Don-t-use-cpumask_equal.patch @@ -0,0 +1,41 @@ +From: Waiman Long <longman@redhat.com> +Date: Thu, 3 Oct 2019 16:36:08 -0400 +Subject: [PATCH 301/342] lib/smp_processor_id: Don't use cpumask_equal() +Origin: https://git.kernel.org/cgit/linux/kernel/git/rt/linux-stable-rt.git/commit?id=83c7d978aa1fe629e0c8c48204de93e5555cdc24 + +[ 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@redhat.com> +Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org> +--- + 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; + + /* |