* the two values of tb_update_count match and are even then the
* tb_to_xs and stamp_xsec values are consistent. If not, then it
* loops back and reads them again until this criteria is met.
+ * We expect the caller to have done the first increment of
+ * vdso_data->tb_update_count already.
*/
- ++(vdso_data->tb_update_count);
- smp_wmb();
vdso_data->tb_orig_stamp = new_tb_stamp;
vdso_data->stamp_xsec = new_stamp_xsec;
vdso_data->tb_to_xs = new_tb_to_xs;
unsigned long offset;
u64 new_stamp_xsec;
u64 tlen, t2x;
+ u64 tb, xsec_old, xsec_new;
+ struct gettimeofday_vars *varp;
if (__USE_RTC())
return;
tlen = current_tick_length();
offset = cur_tb - do_gtod.varp->tb_orig_stamp;
- if (tlen == last_tick_len && offset < 0x80000000u) {
- /* check that we're still in sync; if not, resync */
- struct timeval tv;
- __do_gettimeofday(&tv, cur_tb);
- if (tv.tv_sec <= xtime.tv_sec &&
- (tv.tv_sec < xtime.tv_sec ||
- tv.tv_usec * 1000 <= xtime.tv_nsec))
- return;
- }
+ if (tlen == last_tick_len && offset < 0x80000000u)
+ return;
if (tlen != last_tick_len) {
t2x = mulhdu(tlen << TICKLEN_SHIFT, ticklen_to_xs);
last_tick_len = tlen;
new_stamp_xsec = (u64) xtime.tv_nsec * XSEC_PER_SEC;
do_div(new_stamp_xsec, 1000000000);
new_stamp_xsec += (u64) xtime.tv_sec * XSEC_PER_SEC;
+
+ ++vdso_data->tb_update_count;
+ smp_mb();
+
+ /*
+ * Make sure time doesn't go backwards for userspace gettimeofday.
+ */
+ tb = get_tb();
+ varp = do_gtod.varp;
+ xsec_old = mulhdu(tb - varp->tb_orig_stamp, varp->tb_to_xs)
+ + varp->stamp_xsec;
+ xsec_new = mulhdu(tb - cur_tb, t2x) + new_stamp_xsec;
+ if (xsec_new < xsec_old)
+ new_stamp_xsec += xsec_old - xsec_new;
+
update_gtod(cur_tb, new_stamp_xsec, t2x);
}
}
#endif
+ /* Make userspace gettimeofday spin until we're done. */
+ ++vdso_data->tb_update_count;
+ smp_mb();
+
/*
* Subtract off the number of nanoseconds since the
* beginning of the last tick.
* It is computed as:
* ticklen_to_xs = 2^N / (tb_ticks_per_jiffy * 1e9)
* where N = 64 + 20 - TICKLEN_SCALE - TICKLEN_SHIFT
- * so as to give the result as a 0.64 fixed-point fraction.
+ * which turns out to be N = 51 - SHIFT_HZ.
+ * This gives the result as a 0.64 fixed-point fraction.
+ * That value is reduced by an offset amounting to 1 xsec per
+ * 2^31 timebase ticks to avoid problems with time going backwards
+ * by 1 xsec when we do timer_recalc_offset due to losing the
+ * fractional xsec. That offset is equal to ppc_tb_freq/2^51
+ * since there are 2^20 xsec in a second.
*/
- div128_by_32(1ULL << (64 + 20 - TICKLEN_SCALE - TICKLEN_SHIFT), 0,
- tb_ticks_per_jiffy, &res);
+ div128_by_32((1ULL << 51) - ppc_tb_freq, 0,
+ tb_ticks_per_jiffy << SHIFT_HZ, &res);
div128_by_32(res.result_high, res.result_low, NSEC_PER_SEC, &res);
ticklen_to_xs = res.result_low;