[src/trunk]: src/sys/arch/xen/xen xen_clock(4): Compute NS_PER_TICK only once...

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

details:   https://anonhg.NetBSD.org/src/rev/e14531b5f2ed
branches:  trunk
changeset: 378258:e14531b5f2ed
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Fri Jul 28 10:39:01 2023 +0000

description:
xen_clock(4): Compute NS_PER_TICK only once per call.

This involves a division by an unknown number, so let's cache it.

XXX Could do better by precomputing it in xen_resumeclocks, with some
effort to ensure concurrent calls don't stomp on each other.

diffstat:

 sys/arch/xen/xen/xen_clock.c |  15 ++++++++-------
 1 files changed, 8 insertions(+), 7 deletions(-)

diffs (51 lines):

diff -r 324b01330a50 -r e14531b5f2ed sys/arch/xen/xen/xen_clock.c
--- a/sys/arch/xen/xen/xen_clock.c      Fri Jul 28 10:38:44 2023 +0000
+++ b/sys/arch/xen/xen/xen_clock.c      Fri Jul 28 10:39:01 2023 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: xen_clock.c,v 1.13 2023/07/28 10:38:44 riastradh Exp $ */
+/*     $NetBSD: xen_clock.c,v 1.14 2023/07/28 10:39:01 riastradh Exp $ */
 
 /*-
  * Copyright (c) 2017, 2018 The NetBSD Foundation, Inc.
@@ -36,7 +36,7 @@
 #endif
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: xen_clock.c,v 1.13 2023/07/28 10:38:44 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: xen_clock.c,v 1.14 2023/07/28 10:39:01 riastradh Exp $");
 
 #include <sys/param.h>
 #include <sys/types.h>
@@ -782,6 +782,7 @@ xen_resumeclocks(struct cpu_info *ci)
 static int
 xen_timer_handler(void *cookie, struct clockframe *frame)
 {
+       const uint64_t ns_per_tick = NS_PER_TICK;
        struct cpu_info *ci = curcpu();
        uint64_t last, now, delta, next;
        int error;
@@ -817,11 +818,11 @@ again:
         * times as appears necessary based on how much time has
         * passed.
         */
-       while (delta >= NS_PER_TICK) {
-               ci->ci_xen_hardclock_systime_ns += NS_PER_TICK;
-               delta -= NS_PER_TICK;
+       while (delta >= ns_per_tick) {
+               ci->ci_xen_hardclock_systime_ns += ns_per_tick;
+               delta -= ns_per_tick;
                hardclock(frame);
-               if (__predict_false(delta >= NS_PER_TICK)) {
+               if (__predict_false(delta >= ns_per_tick)) {
                        SDT_PROBE3(sdt, xen, hardclock, missed,
                            last, now, delta);
                        ci->ci_xen_missed_hardclock_evcnt.ev_count++;
@@ -833,7 +834,7 @@ again:
         * time is in the past, so update our idea of what the Xen
         * system time is and try again.
         */
-       next = ci->ci_xen_hardclock_systime_ns + NS_PER_TICK;
+       next = ci->ci_xen_hardclock_systime_ns + ns_per_tick;
        error = HYPERVISOR_set_timer_op(next);
        if (error)
                goto again;