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
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@ -1772,14 +1772,14 @@ pps_capture(struct pps_state *pps)
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#endif
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tc = th->th_counter;
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pps->capcount = tc->tc_get_timecount(tc);
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atomic_thread_fence_acq();
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if (pps->capgen != th->th_generation)
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pps->capgen = 0;
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}
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void
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pps_event(struct pps_state *pps, int event)
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{
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struct timehands *capth;
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struct timecounter *captc;
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uint64_t capth_scale;
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struct bintime bt;
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struct timespec ts, *tsp, *osp;
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u_int tcount, *pcount;
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@ -1798,9 +1798,17 @@ pps_event(struct pps_state *pps, int event)
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/* Nothing to do if not currently set to capture this event type. */
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if ((event & pps->ppsparam.mode) == 0)
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return;
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/* Make a snapshot of the captured timehand */
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capth = pps->capth;
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captc = capth->th_counter;
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capth_scale = capth->th_scale;
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tcount = capth->th_offset_count;
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bt = capth->th_bintime;
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/* If the timecounter was wound up underneath us, bail out. */
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if (pps->capgen == 0 || pps->capgen !=
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atomic_load_acq_int(&pps->capth->th_generation))
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atomic_thread_fence_acq();
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if (pps->capgen == 0 || pps->capgen != capth->th_generation)
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return;
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/* Things would be easier with arrays. */
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@ -1838,25 +1846,19 @@ pps_event(struct pps_state *pps, int event)
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* If the timecounter changed, we cannot compare the count values, so
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* we have to drop the rest of the PPS-stuff until the next event.
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*/
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if (pps->ppstc != pps->capth->th_counter) {
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pps->ppstc = pps->capth->th_counter;
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if (__predict_false(pps->ppstc != captc)) {
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pps->ppstc = captc;
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*pcount = pps->capcount;
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pps->ppscount[2] = pps->capcount;
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return;
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}
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/* Convert the count to a timespec. */
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tcount = pps->capcount - pps->capth->th_offset_count;
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tcount &= pps->capth->th_counter->tc_counter_mask;
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bt = pps->capth->th_bintime;
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bintime_addx(&bt, pps->capth->th_scale * tcount);
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tcount = pps->capcount - tcount;
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tcount &= captc->tc_counter_mask;
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bintime_addx(&bt, capth_scale * tcount);
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bintime2timespec(&bt, &ts);
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/* If the timecounter was wound up underneath us, bail out. */
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atomic_thread_fence_acq();
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if (pps->capgen != pps->capth->th_generation)
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return;
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*pcount = pps->capcount;
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(*pseq)++;
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*tsp = ts;
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@ -1890,9 +1892,9 @@ pps_event(struct pps_state *pps, int event)
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*/
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tcount = pps->capcount - pps->ppscount[2];
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pps->ppscount[2] = pps->capcount;
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tcount &= pps->capth->th_counter->tc_counter_mask;
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tcount &= captc->tc_counter_mask;
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scale = (uint64_t)1 << 63;
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scale /= pps->capth->th_counter->tc_frequency;
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scale /= captc->tc_frequency;
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scale *= 2;
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bt.sec = 0;
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bt.frac = 0;
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