The branch main has been updated by imp:
URL:
https://cgit.FreeBSD.org/src/commit/?id=fd88f4e190bc0a56f8d30179900553ce12d1c0d7
commit fd88f4e190bc0a56f8d30179900553ce12d1c0d7
Author: Sebastian Huber <sebastian.hu...@embedded-brains.de>
AuthorDate: 2023-02-27 21:49:09 +0000
Commit: Warner Losh <i...@freebsd.org>
CommitDate: 2023-02-27 22:10:55 +0000
pps: Simplify capture and event processing
Use local variables for the captured timehand and timecounter in
pps_event().
This fixes a potential issue in the nsec preparation for hardpps(). Here
the
timecounter was accessed through the captured timehand after the generation
was
checked.
Make a snapshot of the relevent timehand values early in pps_event(). Check
the timehand generation only once during the capture and event processing.
Use
atomic_thread_fence_acq() similar to the other readers.
Reviewed by: imp
Pull Request: https://github.com/freebsd/freebsd-src/pull/604
---
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 = th->th_counter;
pps->capcount = tc->tc_get_timecount(tc);
- atomic_thread_fence_acq();
- if (pps->capgen != th->th_generation)
- pps->capgen = 0;
}
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) == 0)
return;
+
+ /* Make a snapshot of the captured timehand */
+ capth = pps->capth;
+ captc = capth->th_counter;
+ capth_scale = capth->th_scale;
+ tcount = capth->th_offset_count;
+ bt = capth->th_bintime;
+
/* If the timecounter was wound up underneath us, bail out. */
- if (pps->capgen == 0 || pps->capgen !=
- atomic_load_acq_int(&pps->capth->th_generation))
+ atomic_thread_fence_acq();
+ if (pps->capgen == 0 || pps->capgen != capth->th_generation)
return;
/* 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 != pps->capth->th_counter) {
- pps->ppstc = pps->capth->th_counter;
+ if (__predict_false(pps->ppstc != captc)) {
+ pps->ppstc = captc;
*pcount = pps->capcount;
pps->ppscount[2] = pps->capcount;
return;
}
/* Convert the count to a timespec. */
- tcount = pps->capcount - pps->capth->th_offset_count;
- tcount &= pps->capth->th_counter->tc_counter_mask;
- bt = pps->capth->th_bintime;
- bintime_addx(&bt, pps->capth->th_scale * tcount);
+ tcount = pps->capcount - tcount;
+ tcount &= captc->tc_counter_mask;
+ bintime_addx(&bt, capth_scale * tcount);
bintime2timespec(&bt, &ts);
- /* If the timecounter was wound up underneath us, bail out. */
- atomic_thread_fence_acq();
- if (pps->capgen != pps->capth->th_generation)
- return;
-
*pcount = pps->capcount;
(*pseq)++;
*tsp = ts;
@@ -1890,9 +1892,9 @@ pps_event(struct pps_state *pps, int event)
*/
tcount = pps->capcount - pps->ppscount[2];
pps->ppscount[2] = pps->capcount;
- tcount &= pps->capth->th_counter->tc_counter_mask;
+ tcount &= captc->tc_counter_mask;
scale = (uint64_t)1 << 63;
- scale /= pps->capth->th_counter->tc_frequency;
+ scale /= captc->tc_frequency;
scale *= 2;
bt.sec = 0;
bt.frac = 0;
