Module Name: src
Committed By: riastradh
Date: Mon Jul 17 21:51:20 UTC 2023
Modified Files:
src/sys/kern: kern_tc.c
Log Message:
timecounter(9): Use seqlock for atomic snapshots of timebase.
To generate a diff of this commit:
cvs rdiff -u -r1.70 -r1.71 src/sys/kern/kern_tc.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/kern/kern_tc.c
diff -u src/sys/kern/kern_tc.c:1.70 src/sys/kern/kern_tc.c:1.71
--- src/sys/kern/kern_tc.c:1.70 Mon Jul 17 15:41:05 2023
+++ src/sys/kern/kern_tc.c Mon Jul 17 21:51:20 2023
@@ -1,4 +1,4 @@
-/* $NetBSD: kern_tc.c,v 1.70 2023/07/17 15:41:05 riastradh Exp $ */
+/* $NetBSD: kern_tc.c,v 1.71 2023/07/17 21:51:20 riastradh Exp $ */
/*-
* Copyright (c) 2008, 2009 The NetBSD Foundation, Inc.
@@ -40,7 +40,7 @@
#include <sys/cdefs.h>
/* __FBSDID("$FreeBSD: src/sys/kern/kern_tc.c,v 1.166 2005/09/19 22:16:31 andre Exp $"); */
-__KERNEL_RCSID(0, "$NetBSD: kern_tc.c,v 1.70 2023/07/17 15:41:05 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_tc.c,v 1.71 2023/07/17 21:51:20 riastradh Exp $");
#ifdef _KERNEL_OPT
#include "opt_ntp.h"
@@ -146,7 +146,10 @@ static volatile struct {
};
#endif
-static struct bintime timebasebin;
+static struct {
+ struct bintime bin;
+ volatile unsigned gen; /* even when stable, odd when changing */
+} timebase __cacheline_aligned;
static int timestepwarnings;
@@ -496,10 +499,12 @@ microuptime(struct timeval *tvp)
void
bintime(struct bintime *bt)
{
+ struct bintime boottime;
TC_COUNT(nbintime);
binuptime(bt);
- bintime_add(bt, &timebasebin);
+ getbinboottime(&boottime);
+ bintime_add(bt, &boottime);
}
void
@@ -568,6 +573,7 @@ void
getbintime(struct bintime *bt)
{
struct timehands *th;
+ struct bintime boottime;
u_int gen;
TC_COUNT(ngetbintime);
@@ -576,7 +582,8 @@ getbintime(struct bintime *bt)
gen = th->th_generation;
*bt = th->th_offset;
} while (gen == 0 || gen != th->th_generation);
- bintime_add(bt, &timebasebin);
+ getbinboottime(&boottime);
+ bintime_add(bt, &boottime);
}
static inline void
@@ -642,14 +649,25 @@ getmicroboottime(struct timeval *tvp)
}
void
-getbinboottime(struct bintime *bt)
+getbinboottime(struct bintime *basep)
{
+ struct bintime base;
+ unsigned gen;
- /*
- * XXX Need lockless read synchronization around timebasebin
- * (and not just here).
- */
- *bt = timebasebin;
+ do {
+ /* Spin until the timebase isn't changing. */
+ while ((gen = atomic_load_relaxed(&timebase.gen)) & 1)
+ SPINLOCK_BACKOFF_HOOK;
+
+ /* Read out a snapshot of the timebase. */
+ membar_consumer();
+ base = timebase.bin;
+ membar_consumer();
+
+ /* Restart if it changed while we were reading. */
+ } while (gen != atomic_load_relaxed(&timebase.gen));
+
+ *basep = base;
}
/*
@@ -839,8 +857,12 @@ tc_setclock(const struct timespec *ts)
binuptime(&bt2);
timespec2bintime(ts, &bt);
bintime_sub(&bt, &bt2);
- bintime_add(&bt2, &timebasebin);
- timebasebin = bt;
+ bintime_add(&bt2, &timebase.bin);
+ timebase.gen |= 1; /* change in progress */
+ membar_producer();
+ timebase.bin = bt;
+ membar_producer();
+ timebase.gen++; /* commit change */
tc_windup();
mutex_spin_exit(&timecounter_lock);
@@ -921,7 +943,7 @@ tc_windup(void)
* the adjustment resulting from adjtime() calls.
*/
bt = th->th_offset;
- bintime_add(&bt, &timebasebin);
+ bintime_add(&bt, &timebase.bin);
i = bt.sec - tho->th_microtime.tv_sec;
if (i > LARGE_STEP)
i = 2;
@@ -929,8 +951,13 @@ tc_windup(void)
t = bt.sec;
ntp_update_second(&th->th_adjustment, &bt.sec);
s_update = 1;
- if (bt.sec != t)
- timebasebin.sec += bt.sec - t;
+ if (bt.sec != t) {
+ timebase.gen |= 1; /* change in progress */
+ membar_producer();
+ timebase.bin.sec += bt.sec - t;
+ membar_producer();
+ timebase.gen++; /* commit change */
+ }
}
/* Update the UTC timestamps used by the get*() functions. */
@@ -1273,7 +1300,7 @@ pps_ref_event(struct pps_state *pps,
/* Convert the count to a bintime. */
bt = pps->capth->th_offset;
bintime_addx(&bt, pps->capth->th_scale * (acount - pps->capth->th_offset_count));
- bintime_add(&bt, &timebasebin);
+ bintime_add(&bt, &timebase.bin);
if ((refmode & PPS_REFEVNT_PPS) == 0) {
/* determine difference to reference time stamp */
