| Message ID | alpine.DEB.2.11.1510221133590.4012@nanos (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 2015/10/22 18:25, Thomas Gleixner wrote: > On Thu, 22 Oct 2015, Ding Tianhong wrote: >> On 2015/10/22 15:43, Thomas Gleixner wrote: >>>> Jan 01 00:03:32 Linux kernel: i:0 basenow.tv64:4809284991830 >>>> hrtimer_get_softexpires_tv64(timer):4440120000000 ccpu0 >>>> timer:ffffffdffdec6138, timer->function:ffffffc000129b84 >>>> Jan 01 00:03:32 Linux kernel: i:0 basenow.tv64:4809284991830 >>>> hrtimer_get_softexpires_tv64(timer):4440120000000 ccpu0 > >> This problem could only occur on the system with 32 cores, when I >> cut the cores to 16, this problem disappeared, so I think there is >> some parallel problem when the 32 core set clock time together: > >> I try to reproduce the scene: >> >> 1.do_settimeofday64 >> 2.update tk time >> 3.update base time offset >> 4.update expires_next >> >> the 3 and 4 will be called in softirq, but the hrtimer_interrupt may >> break the order and run before 3, I am not sure whether this could >> make the problem, do we need to update base time and expires_next in >> the hrtimer_interrupt? maybe I miss something, thanks for any >> suggestion. > > Base offset is updated in hrtimer_interrupt as > well. hrtimer_update_base() does that. So that's not the problem. > > Can you apply the patch below and enable the hrtimer tracepoints and > collect trace data across the point where the problem happens? > > Thanks, > > tglx > ---- > > diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c > index 44d2cc0436f4..614f8d272cb0 100644 > --- a/kernel/time/timekeeping.c > +++ b/kernel/time/timekeeping.c > @@ -575,8 +575,14 @@ static void timekeeping_update(struct timekeeper *tk, unsigned int action) > update_fast_timekeeper(&tk->tkr_mono, &tk_fast_mono); > update_fast_timekeeper(&tk->tkr_raw, &tk_fast_raw); > > - if (action & TK_CLOCK_WAS_SET) > + if (action & TK_CLOCK_WAS_SET) { > tk->clock_was_set_seq++; > + trace_printk("TK: Seq: %u R: %lld B: %lld T: %lld\n", > + tk->clock_was_set_seq, > + tk->offs_real, > + tk->offs_boot, > + tk->offs_tai); > + } > /* > * The mirroring of the data to the shadow-timekeeper needs > * to happen last here to ensure we don't over-write the > @@ -1954,6 +1960,11 @@ ktime_t ktime_get_update_offsets_now(unsigned int *cwsseq, ktime_t *offs_real, > base = ktime_add_ns(base, nsecs); > > if (*cwsseq != tk->clock_was_set_seq) { > + trace_printk("HR: Seq: %u R: %lld B: %lld T: %lld\n", > + tk->clock_was_set_seq, > + tk->offs_real, > + tk->offs_boot, > + tk->offs_tai); > *cwsseq = tk->clock_was_set_seq; > *offs_real = tk->offs_real; > *offs_boot = tk->offs_boot; > > . > I don't try this patch yet. But I found out when the cpu is stalling, basenow.tv64(7676664221321) is bigger than ktime_get().tv64(7336008904750) in hrtimer_interrupt() and the timer->_softexpires is 7336288000000. This makes it can not finish the while loop until ktime_get().tv64 arrives basenow.tv64. Is it correct that basenow bigger than ktime_get() ? Thanks, Yang
On Thu, 22 Oct 2015, Yang Yingliang wrote: > But I found out when the cpu is stalling, basenow.tv64(7676664221321) is > bigger than ktime_get().tv64(7336008904750) in hrtimer_interrupt() and > the timer->_softexpires is 7336288000000. This makes it can not finish > the while loop until ktime_get().tv64 arrives basenow.tv64. > > Is it correct that basenow bigger than ktime_get() ? You only can compare basenow and ktime_get() for the clock monotonic base. If you are actually observing this on clock monotonic base then base->offset of clock monotonic is not 0, which should never happen. Thanks, tglx
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 44d2cc0436f4..614f8d272cb0 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -575,8 +575,14 @@ static void timekeeping_update(struct timekeeper *tk, unsigned int action) update_fast_timekeeper(&tk->tkr_mono, &tk_fast_mono); update_fast_timekeeper(&tk->tkr_raw, &tk_fast_raw); - if (action & TK_CLOCK_WAS_SET) + if (action & TK_CLOCK_WAS_SET) { tk->clock_was_set_seq++; + trace_printk("TK: Seq: %u R: %lld B: %lld T: %lld\n", + tk->clock_was_set_seq, + tk->offs_real, + tk->offs_boot, + tk->offs_tai); + } /* * The mirroring of the data to the shadow-timekeeper needs * to happen last here to ensure we don't over-write the @@ -1954,6 +1960,11 @@ ktime_t ktime_get_update_offsets_now(unsigned int *cwsseq, ktime_t *offs_real, base = ktime_add_ns(base, nsecs); if (*cwsseq != tk->clock_was_set_seq) { + trace_printk("HR: Seq: %u R: %lld B: %lld T: %lld\n", + tk->clock_was_set_seq, + tk->offs_real, + tk->offs_boot, + tk->offs_tai); *cwsseq = tk->clock_was_set_seq; *offs_real = tk->offs_real; *offs_boot = tk->offs_boot;