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diff --git a/sys/kern/kern_ffclock.c b/sys/kern/kern_ffclock.c
--- a/sys/kern/kern_ffclock.c
+++ b/sys/kern/kern_ffclock.c
@@ -231,7 +231,7 @@
sysctl_kern_sysclock_active, "A",
"Name of the active system clock which is currently serving time");
-static int sysctl_kern_ffclock_ffcounter_bypass = 0;
+int sysctl_kern_ffclock_ffcounter_bypass = 0;
SYSCTL_INT(_kern_sysclock_ffclock, OID_AUTO, ffcounter_bypass, CTLFLAG_RW,
&sysctl_kern_ffclock_ffcounter_bypass, 0,
"Use reliable hardware timecounter as the feedforward counter");
diff --git a/sys/kern/kern_tc.c b/sys/kern/kern_tc.c
--- a/sys/kern/kern_tc.c
+++ b/sys/kern/kern_tc.c
@@ -762,38 +762,57 @@
}
/*
- * Adjust the fftimehands when the timecounter is changed. Stating the obvious,
- * the old and new hardware counter cannot be read simultaneously. tc_windup()
- * does read the two counters 'back to back', but a few cycles are effectively
- * lost, and not accumulated in tick_ffcount. This is a fairly radical
- * operation for a feedforward synchronization daemon, and it is its job to not
- * pushing irrelevant data to the kernel. Because there is no locking here,
- * simply force to ignore pending or next update to give daemon a chance to
- * realize the counter has changed.
+ * Adjust fftimehands when the timecounter is changed.
+ * This update does not advance the tick itself (hence UTC members remain
+ * valid), rather values are reinitiated when not relevant for the new counter.
+ * Because there is no locking here, simply force to ignore pending or next
+ * update to give daemon a chance to realize the counter has changed.
*/
static void
-ffclock_change_tc(struct timehands *th)
+ffclock_change_tc(struct timehands *th, unsigned int ncount)
{
struct fftimehands *ffth;
struct ffclock_estimate *cest;
struct timecounter *tc;
uint8_t ogen;
+ ffcounter now;
tc = th->th_counter;
+
+ /* Prepare next fftimehand where tick state will be updated. */
ffth = fftimehands->next;
ogen = ffth->gen;
ffth->gen = 0;
-
cest = &ffth->cest;
+
+ /*
+ * Origin setting: reset FFcounter to match start of the current tick.
+ * If a TSC-derived counter, get correct higher order bits to ensure the
+ * FFcounter origin matches that of the true counter, rather than the
+ * time the counter was adopted. If not TSC-derived, the origin will be
+ * ncount in the past. In all cases, the lower bits of FFcounter and
+ * th_offset_count will agree.
+ */
+ if ( strcmp(tc->tc_name, "TSC") != 0 )
+ ffth->tick_ffcount = (ffcounter)ncount;
+ else {
+ now = (ffcounter) rdtsc();
+ if (strcmp(tc->tc_name, "TSC-low") == 0) // TSC reads shifted
+ now >>= (int)(intptr_t)tc->tc_priv;
+ /* Reconstruct counter value at the time ncount was taken. */
+ ffth->tick_ffcount = now -
+ (ffcounter)((unsigned int)now - ncount);
+ }
+
memcpy(cest, &(fftimehands->cest), sizeof(struct ffclock_estimate));
+ cest->update_ffcount = ffth->tick_ffcount;
cest->period = ((1ULL << 63) / tc->tc_frequency ) << 1;
cest->errb_abs = 0;
cest->errb_rate = 0;
cest->status |= FFCLOCK_STA_UNSYNC;
- ffth->tick_ffcount = fftimehands->tick_ffcount;
- ffth->tick_time_lerp = fftimehands->tick_time_lerp;
ffth->tick_time = fftimehands->tick_time;
+ ffth->tick_time_lerp = fftimehands->tick_time_lerp;
ffth->period_lerp = cest->period;
/* Do not lock but ignore next update from synchronization daemon. */
@@ -803,6 +822,12 @@
ogen = 1;
ffth->gen = ogen;
fftimehands = ffth;
+
+ printf("ffclock_change_tc: new tick_ffcount = %llu = %#llX, with "
+ "tc %s (%llu Hz)\n",
+ (unsigned long long)ffth->tick_ffcount,
+ (unsigned long long)ffth->tick_ffcount,
+ tc->tc_name, (unsigned long long)tc->tc_frequency);
}
/*
@@ -893,6 +918,7 @@
/*
* Access to current ffcounter value.
+ * If bypass mode on, assume the counter is TSC, and access it directly.
*/
void
ffclock_read_counter(ffcounter *ffcount)
@@ -901,6 +927,11 @@
struct fftimehands *ffth;
unsigned int gen, delta;
+ if (sysctl_kern_ffclock_ffcounter_bypass == 1) {
+ *ffcount = (ffcounter) rdtsc();
+ return;
+ }
+
/*
* ffclock_windup() called from tc_windup(), safe to rely on
* th->th_generation only, for correct delta and ffcounter.
@@ -1040,9 +1071,13 @@
extern long time_esterror;
/*
- * Take a raw timestamp (timecounter reading), and then snapshot the sysclock
- * data which can be used to compare system clocks and generate timestamps
- * of all possible types after the fact.
+ * Take a raw timestamp (timecounter reading) as soon as possible, then snapshot
+ * the state of both FB and FF clocks, and the sysclock. The collected state can
+ * be used to fairly compare alternative system clocks on a precise shared event
+ * (the raw timestamp) as well as to generate timestamps of all possible types
+ * at any later time, unaffected by the delay in so doing. If bypass mode is
+ * on, assume the counter is a TSC variant, and access it directly for reduced
+ * timestamping latency and overhead.
*/
void
sysclock_getsnapshot(struct sysclock_snap *clock_snap, int fast)
@@ -1053,22 +1088,29 @@
unsigned int delta, gen;
#ifdef FFCLOCK
ffcounter ffcount;
- struct fftimehands *ffth;
struct ffclock_info *ffi;
+ struct fftimehands *ffth;
struct ffclock_estimate cest;
-
- ffi = &clock_snap->ff_info;
#endif
- fbi = &clock_snap->fb_info;
delta = 0;
do {
th = timehands;
gen = atomic_load_acq_int(&th->th_generation);
+ if (!fast) {
+#ifdef FFCLOCK
+ if (sysctl_kern_ffclock_ffcounter_bypass == 1)
+ delta = rdtsc32() - th->th_offset_count;
+ else
+#endif
+ delta = tc_delta(th);
+ }
+ fbi = &clock_snap->fb_info;
fbi->th_scale = th->th_scale;
fbi->tick_time = th->th_offset;
#ifdef FFCLOCK
+ ffi = &clock_snap->ff_info;
ffth = fftimehands;
ffi->tick_time = ffth->tick_time;
ffi->tick_time_lerp = ffth->tick_time_lerp;
@@ -1077,8 +1119,6 @@
clock_snap->ffcount = ffth->tick_ffcount;
cest = ffth->cest;
#endif
- if (!fast)
- delta = tc_delta(th);
atomic_thread_fence_acq();
} while (gen == 0 || gen != th->th_generation);
@@ -1461,6 +1501,9 @@
/* Now is a good time to change timecounters. */
if (th->th_counter != tc) {
+ printf("Changing tc counter : %s = %#X --> %s = %#X \n",
+ th->th_counter->tc_name, th->th_offset_count,
+ tc->tc_name, ncount);
#ifndef __arm__
if ((tc->tc_flags & TC_FLAGS_C2STOP) != 0)
cpu_disable_c2_sleep++;
@@ -1473,7 +1516,7 @@
(((uint64_t)tc->tc_counter_mask + 1) / 3));
recalculate_scaling_factor_and_large_delta(th);
#ifdef FFCLOCK
- ffclock_change_tc(th);
+ ffclock_change_tc(th, ncount);
#endif
}
diff --git a/sys/sys/timeffc.h b/sys/sys/timeffc.h
--- a/sys/sys/timeffc.h
+++ b/sys/sys/timeffc.h
@@ -68,6 +68,13 @@
/* Declare the kern.sysclock.ffclock sysctl tree. */
SYSCTL_DECL(_kern_sysclock_ffclock);
+/* Flag defining if counter bypass mode is desired or not.
+ * This is only possible if the counter is a TSC with rdtsc defined.
+ */
+#ifdef FFCLOCK
+extern int sysctl_kern_ffclock_ffcounter_bypass;
+#endif
+
/*
* Index into the sysclocks array for obtaining the ASCII name of a particular
* sysclock.

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