[src/trunk]: src/sys/kern Break the slow path for callout_halt() out into its...

[ad <ad%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/a80a9d001add
branches:  trunk
changeset: 966894:a80a9d001add
user:      ad <ad%NetBSD.org@localhost>
date:      Thu Nov 21 17:57:40 2019 +0000

description:
Break the slow path for callout_halt() out into its own routine.
No functional change.

diffstat:

 sys/kern/kern_timeout.c |  50 +++++++++++++++++++++++++++++++++---------------
 1 files changed, 34 insertions(+), 16 deletions(-)

diffs (96 lines):

diff -r e62cc3e39f2e -r a80a9d001add sys/kern/kern_timeout.c
--- a/sys/kern/kern_timeout.c   Thu Nov 21 17:54:04 2019 +0000
+++ b/sys/kern/kern_timeout.c   Thu Nov 21 17:57:40 2019 +0000
@@ -1,7 +1,7 @@
-/*     $NetBSD: kern_timeout.c,v 1.56 2019/03/10 13:44:49 kre Exp $    */
+/*     $NetBSD: kern_timeout.c,v 1.57 2019/11/21 17:57:40 ad Exp $     */
 
 /*-
- * Copyright (c) 2003, 2006, 2007, 2008, 2009 The NetBSD Foundation, Inc.
+ * Copyright (c) 2003, 2006, 2007, 2008, 2009, 2019 The NetBSD Foundation, Inc.
  * All rights reserved.
  *
  * This code is derived from software contributed to The NetBSD Foundation
@@ -59,7 +59,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_timeout.c,v 1.56 2019/03/10 13:44:49 kre Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_timeout.c,v 1.57 2019/11/21 17:57:40 ad Exp $");
 
 /*
  * Timeouts are kept in a hierarchical timing wheel.  The c_time is the
@@ -185,8 +185,10 @@
 #ifndef CRASH
 
 static void    callout_softclock(void *);
-static struct callout_cpu callout_cpu0;
-static void *callout_sih;
+static void    callout_wait(callout_impl_t *, void *, kmutex_t *);
+
+static struct callout_cpu callout_cpu0 __cacheline_aligned;
+static void *callout_sih __read_mostly;
 
 static inline kmutex_t *
 callout_lock(callout_impl_t *c)
@@ -466,24 +468,42 @@
 callout_halt(callout_t *cs, void *interlock)
 {
        callout_impl_t *c = (callout_impl_t *)cs;
-       struct callout_cpu *cc;
-       struct lwp *l;
-       kmutex_t *lock, *relock;
-       bool expired;
+       kmutex_t *lock;
+       int flags;
 
        KASSERT(c->c_magic == CALLOUT_MAGIC);
        KASSERT(!cpu_intr_p());
        KASSERT(interlock == NULL || mutex_owned(interlock));
 
+       /* Fast path. */
        lock = callout_lock(c);
-       relock = NULL;
+       flags = c->c_flags;
+       if ((flags & CALLOUT_PENDING) != 0)
+               CIRCQ_REMOVE(&c->c_list);
+       c->c_flags = flags & ~(CALLOUT_PENDING|CALLOUT_FIRED);
+       if (__predict_false(flags & CALLOUT_FIRED)) {
+               callout_wait(c, interlock, lock);
+               return true;
+       }
+       mutex_spin_exit(lock);
+       return false;
+}
 
-       expired = ((c->c_flags & CALLOUT_FIRED) != 0);
-       if ((c->c_flags & CALLOUT_PENDING) != 0)
-               CIRCQ_REMOVE(&c->c_list);
-       c->c_flags &= ~(CALLOUT_PENDING|CALLOUT_FIRED);
+/*
+ * callout_wait:
+ *
+ *     Slow path for callout_halt().  Deliberately marked __noinline to
+ *     prevent unneeded overhead in the caller.
+ */
+static void __noinline
+callout_wait(callout_impl_t *c, void *interlock, kmutex_t *lock)
+{
+       struct callout_cpu *cc;
+       struct lwp *l;
+       kmutex_t *relock;
 
        l = curlwp;
+       relock = NULL;
        for (;;) {
                cc = c->c_cpu;
                if (__predict_true(cc->cc_active != c || cc->cc_lwp == l))
@@ -515,8 +535,6 @@
        mutex_spin_exit(lock);
        if (__predict_false(relock != NULL))
                mutex_enter(relock);
-
-       return expired;
 }
 
 #ifdef notyet