From e68ccbe85eedeaba3b4026cd96289af8bb00cc28 Mon Sep 17 00:00:00 2001 From: Attilio Rao Date: Sun, 9 Dec 2012 04:54:22 +0000 Subject: [PATCH] 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 --- sys/kern/kern_switch.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/sys/kern/kern_switch.c b/sys/kern/kern_switch.c index 885dc22cea76..d0009b1042f3 100644 --- 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)