Add a comment on why inlining critical_enter() may not be a good idea

for the general case. Reviewed by: bde MFC after: 1 week
svn path=/head/; revision=244046
2012-12-09 04:54:22 +00:00 · 2012-12-09 04:54:22 +00:00 · e68ccbe85e · 2020-12-20 02:59:44 +00:00
commit e68ccbe85e
parent 25b5bb4c1b
1 changed files with 6 additions and 0 deletions
--- a/sys/kern/kern_switch.c
+++ b/sys/kern/kern_switch.c
@ -176,6 +176,12 @@ choosethread(void)
 /*
 * Kernel thread preemption implementation.  Critical sections mark
 * regions of code in which preemptions are not allowed.
+ *
+ * It might seem a good idea to inline critical_enter() but, in order
+ * to prevent instructions reordering by the compiler, a __compiler_membar()
+ * would have to be used here (the same as sched_pin()).  The performance
+ * penalty imposed by the membar could, then, produce slower code than
+ * the function call itself, for most cases.
 */
 void
 critical_enter(void)