[src/trunk]: src/sys/arch xen: Record event when local view of timecounter is...

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

details:   https://anonhg.NetBSD.org/src/rev/52639445a9f6
branches:  trunk
changeset: 377469:52639445a9f6
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Thu Jul 13 13:34:15 2023 +0000

description:
xen: Record event when local view of timecounter is behind global.

diffstat:

 sys/arch/x86/include/cpu.h   |   3 ++-
 sys/arch/xen/xen/xen_clock.c |  33 ++++++++++++++++++++++++++-------
 2 files changed, 28 insertions(+), 8 deletions(-)

diffs (95 lines):

diff -r 385e545271fb -r 52639445a9f6 sys/arch/x86/include/cpu.h
--- a/sys/arch/x86/include/cpu.h        Thu Jul 13 13:33:55 2023 +0000
+++ b/sys/arch/x86/include/cpu.h        Thu Jul 13 13:34:15 2023 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: cpu.h,v 1.134 2023/07/13 12:06:20 riastradh Exp $      */
+/*     $NetBSD: cpu.h,v 1.135 2023/07/13 13:34:15 riastradh Exp $      */
 
 /*
  * Copyright (c) 1990 The Regents of the University of California.
@@ -325,6 +325,7 @@ struct cpu_info {
        struct evcnt    ci_xen_raw_systime_backwards_evcnt;
        struct evcnt    ci_xen_systime_backwards_hardclock_evcnt;
        struct evcnt    ci_xen_missed_hardclock_evcnt;
+       struct evcnt    ci_xen_timecounter_backwards_evcnt;
 #endif /* XEN */
 
 #if defined(GPROF) && defined(MULTIPROCESSOR)
diff -r 385e545271fb -r 52639445a9f6 sys/arch/xen/xen/xen_clock.c
--- a/sys/arch/xen/xen/xen_clock.c      Thu Jul 13 13:33:55 2023 +0000
+++ b/sys/arch/xen/xen/xen_clock.c      Thu Jul 13 13:34:15 2023 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: xen_clock.c,v 1.10 2023/07/07 15:13:41 bouyer Exp $    */
+/*     $NetBSD: xen_clock.c,v 1.11 2023/07/13 13:34:15 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 1.10 2023/07/07 15:13:41 bouyer Exp $");
+__KERNEL_RCSID(0, "$NetBSD: xen_clock.c,v 1.11 2023/07/13 13:34:15 riastradh Exp $");
 
 #include <sys/param.h>
 #include <sys/types.h>
@@ -112,6 +112,11 @@ SDT_PROBE_DEFINE7(sdt, xen, clock, systi
     "uint64_t"/*tsc*/,
     "uint64_t"/*systime_ns*/);
 
+SDT_PROBE_DEFINE3(sdt, xen, timecounter, backward,
+    "uint64_t"/*local*/,
+    "uint64_t"/*skew*/,
+    "uint64_t"/*global*/);
+
 SDT_PROBE_DEFINE2(sdt, xen, hardclock, systime__backward,
     "uint64_t"/*last_systime_ns*/,
     "uint64_t"/*this_systime_ns*/);
@@ -510,7 +515,7 @@ static uint64_t
 xen_global_systime_ns(void)
 {
        struct cpu_info *ci;
-       uint64_t local, global, result;
+       uint64_t local, global, skew, result;
 
        /*
         * Find the local timecount on this CPU, and make sure it does
@@ -524,13 +529,24 @@ xen_global_systime_ns(void)
        ci = curcpu();
        do {
                local = xen_vcputime_systime_ns();
-               local += ci->ci_xen_systime_ns_skew;
+               skew = ci->ci_xen_systime_ns_skew;
                global = xen_global_systime_ns_stamp;
-               if (__predict_false(local < global + 1)) {
+               if (__predict_false(local + skew < global + 1)) {
+                       SDT_PROBE3(sdt, xen, timecounter, backward,
+                           local, skew, global);
+#if XEN_CLOCK_DEBUG
+                       device_printf(ci->ci_dev,
+                           "xen timecounter went backwards:"
+                           " local=%"PRIu64" skew=%"PRIu64" global=%"PRIu64","
+                           " adding %"PRIu64" to skew\n",
+                           local, skew, global, global + 1 - (local + skew));
+#endif
+                       ci->ci_xen_timecounter_backwards_evcnt.ev_count++;
                        result = global + 1;
-                       ci->ci_xen_systime_ns_skew += global + 1 - local;
+                       ci->ci_xen_systime_ns_skew += global + 1 -
+                           (local + skew);
                } else {
-                       result = local;
+                       result = local + skew;
                }
        } while (atomic_cas_64(&xen_global_systime_ns_stamp, global, result)
            != global);
@@ -831,6 +847,9 @@ xen_initclocks(void)
        evcnt_attach_dynamic(&ci->ci_xen_missed_hardclock_evcnt,
            EVCNT_TYPE_INTR, NULL, device_xname(ci->ci_dev),
            "missed hardclock");
+       evcnt_attach_dynamic(&ci->ci_xen_timecounter_backwards_evcnt,
+           EVCNT_TYPE_INTR, NULL, device_xname(ci->ci_dev),
+           "timecounter went backwards");
 
        /* Fire up the clocks.  */
        xen_resumeclocks(ci);