[src/trunk]: src/sys/arch/x86/x86 Fix TSC drift is observed almost every time...

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

details:   https://anonhg.NetBSD.org/src/rev/caa7cb4932bc
branches:  trunk
changeset: 850362:caa7cb4932bc
user:      knakahara <knakahara%NetBSD.org@localhost>
date:      Fri Apr 03 03:05:39 2020 +0000

description:
Fix TSC drift is observed almost every time wrongly.

Ths "TSC drift" in tsc_tc_init() means the cpu_cc_skew delta between
first measurement (in cpu_start_secondary) and second measurement
(in cpu_boot_secondary), that is, the TSC drift is expected to be
almost zero.  However, the second measument in current implementation
is added extra cpu_cc_skew accidentally, so current delta value means
almost cpu_cc_skew wrongly.

tsc_sync_bp and tsc_sync_ap should use rdtsc() to get raw values.

Advised by nonaka@n.o, thanks.

diffstat:

 sys/arch/x86/x86/tsc.c |  12 ++++++------
 1 files changed, 6 insertions(+), 6 deletions(-)

diffs (48 lines):

diff -r 8de910bc95c4 -r caa7cb4932bc sys/arch/x86/x86/tsc.c
--- a/sys/arch/x86/x86/tsc.c    Thu Apr 02 21:36:03 2020 +0000
+++ b/sys/arch/x86/x86/tsc.c    Fri Apr 03 03:05:39 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: tsc.c,v 1.38 2020/02/21 00:26:22 joerg Exp $   */
+/*     $NetBSD: tsc.c,v 1.39 2020/04/03 03:05:39 knakahara Exp $       */
 
 /*-
  * Copyright (c) 2008 The NetBSD Foundation, Inc.
@@ -27,7 +27,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: tsc.c,v 1.38 2020/02/21 00:26:22 joerg Exp $");
+__KERNEL_RCSID(0, "$NetBSD: tsc.c,v 1.39 2020/04/03 03:05:39 knakahara Exp $");
 
 #include <sys/param.h>
 #include <sys/systm.h>
@@ -201,13 +201,13 @@
 
        /* Flag it and read our TSC. */
        atomic_or_uint(&ci->ci_flags, CPUF_SYNCTSC);
-       bptsc = cpu_counter_serializing() >> 1;
+       bptsc = (rdtsc() >> 1);
 
        /* Wait for remote to complete, and read ours again. */
        while ((ci->ci_flags & CPUF_SYNCTSC) != 0) {
                __insn_barrier();
        }
-       bptsc += (cpu_counter_serializing() >> 1);
+       bptsc += (rdtsc() >> 1);
 
        /* Wait for the results to come in. */
        while (tsc_sync_cpu == ci) {
@@ -246,11 +246,11 @@
        while ((ci->ci_flags & CPUF_SYNCTSC) == 0) {
                __insn_barrier();
        }
-       tsc = (cpu_counter_serializing() >> 1);
+       tsc = (rdtsc() >> 1);
 
        /* Instruct primary to read its counter. */
        atomic_and_uint(&ci->ci_flags, ~CPUF_SYNCTSC);
-       tsc += (cpu_counter_serializing() >> 1);
+       tsc += (rdtsc() >> 1);
 
        /* Post result.  Ensure the whole value goes out atomically. */
        (void)atomic_swap_64(&tsc_sync_val, tsc);