Date: Thu, 7 Jul 2022 17:25:02 +0200 From: Sebastian Huber <sebastian.huber@embedded-brains.de> To: freebsd-hackers@freebsd.org Subject: [PATCH 2/6] pps: Simplify capture and event processing Message-ID: <20220707152506.55626-3-sebastian.huber@embedded-brains.de> In-Reply-To: <20220707152506.55626-1-sebastian.huber@embedded-brains.de> References: <20220707152506.55626-1-sebastian.huber@embedded-brains.de>
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Use local variables for the captured timehand and timecounter in pps_even=
t().
This fixes a potential issue in the nsec preparation for hardpps(). Here=
the
timecounter was accessed through the captured timehand after the generati=
on was
checked.
Make a snapshot of the relevent timehand values early in pps_event(). Ch=
eck
the timehand generation only once during the capture and event processing=
. Use
atomic_thread_fence_acq() similar to the other readers.
---
sys/kern/kern_tc.c | 38 ++++++++++++++++++++------------------
1 file changed, 20 insertions(+), 18 deletions(-)
diff --git a/sys/kern/kern_tc.c b/sys/kern/kern_tc.c
index 20520adc0aba..b466fd4399e4 100644
--- a/sys/kern/kern_tc.c
+++ b/sys/kern/kern_tc.c
@@ -1772,14 +1772,14 @@ pps_capture(struct pps_state *pps)
#endif
tc =3D th->th_counter;
pps->capcount =3D tc->tc_get_timecount(tc);
- atomic_thread_fence_acq();
- if (pps->capgen !=3D th->th_generation)
- pps->capgen =3D 0;
}
=20
void
pps_event(struct pps_state *pps, int event)
{
+ struct timehands *capth;
+ struct timecounter *captc;
+ uint64_t capth_scale;
struct bintime bt;
struct timespec ts, *tsp, *osp;
u_int tcount, *pcount;
@@ -1798,9 +1798,17 @@ pps_event(struct pps_state *pps, int event)
/* Nothing to do if not currently set to capture this event type. */
if ((event & pps->ppsparam.mode) =3D=3D 0)
return;
+
+ /* Make a snapshot of the captured timehand */
+ capth =3D pps->capth;
+ captc =3D capth->th_counter;
+ capth_scale =3D capth->th_scale;
+ tcount =3D capth->th_offset_count;
+ bt =3D capth->th_bintime;
+
/* If the timecounter was wound up underneath us, bail out. */
- if (pps->capgen =3D=3D 0 || pps->capgen !=3D
- atomic_load_acq_int(&pps->capth->th_generation))
+ atomic_thread_fence_acq();
+ if (pps->capgen =3D=3D 0 || pps->capgen !=3D capth->th_generation)
return;
=20
/* Things would be easier with arrays. */
@@ -1838,25 +1846,19 @@ pps_event(struct pps_state *pps, int event)
* If the timecounter changed, we cannot compare the count values, so
* we have to drop the rest of the PPS-stuff until the next event.
*/
- if (pps->ppstc !=3D pps->capth->th_counter) {
- pps->ppstc =3D pps->capth->th_counter;
+ if (__predict_false(pps->ppstc !=3D captc)) {
+ pps->ppstc =3D captc;
*pcount =3D pps->capcount;
pps->ppscount[2] =3D pps->capcount;
return;
}
=20
/* Convert the count to a timespec. */
- tcount =3D pps->capcount - pps->capth->th_offset_count;
- tcount &=3D pps->capth->th_counter->tc_counter_mask;
- bt =3D pps->capth->th_bintime;
- bintime_addx(&bt, pps->capth->th_scale * tcount);
+ tcount =3D pps->capcount - tcount;
+ tcount &=3D captc->tc_counter_mask;
+ bintime_addx(&bt, capth_scale * tcount);
bintime2timespec(&bt, &ts);
=20
- /* If the timecounter was wound up underneath us, bail out. */
- atomic_thread_fence_acq();
- if (pps->capgen !=3D pps->capth->th_generation)
- return;
-
*pcount =3D pps->capcount;
(*pseq)++;
*tsp =3D ts;
@@ -1890,9 +1892,9 @@ pps_event(struct pps_state *pps, int event)
*/
tcount =3D pps->capcount - pps->ppscount[2];
pps->ppscount[2] =3D pps->capcount;
- tcount &=3D pps->capth->th_counter->tc_counter_mask;
+ tcount &=3D captc->tc_counter_mask;
scale =3D (uint64_t)1 << 63;
- scale /=3D pps->capth->th_counter->tc_frequency;
+ scale /=3D captc->tc_frequency;
scale *=3D 2;
bt.sec =3D 0;
bt.frac =3D 0;
--=20
2.35.3
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