Messages in this thread | | | Date | Tue, 26 Jan 2016 16:21:01 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [PATCH] nohz: fix jiffies warp while switch to low-res nohz mode |
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On Thu, 21 Jan 2016, Wanpeng Li wrote:
> After commit 0ff53d096422 ("tick: sched: Force tick interrupt and get rid > of softirq magic"), next expire time is overwritten by last_jiffies_update > while switch to low-res nohz mode which leads to jiffies warp. This patch > fix it by programming ce device the expire time in the future.
> - hrtimer_forward_now(&ts->sched_timer, tick_period); > hrtimer_set_expires(&ts->sched_timer, next); > - tick_program_event(next, 1); > + hrtimer_forward_now(&ts->sched_timer, tick_period); > + tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1); > tick_nohz_activate(ts, NOHZ_MODE_LOWRES);
I agree, that the ordering forward/set is wrong and needs to be fixed, but how does that result in a jiffies warp?
tick_nohz_handler() tick_sched_do_timer() tick_do_update_jiffies64() delta = ktime_sub(now, last_jiffies_update); if (delta.tv64 < tick_period.tv64) return;
So if that timer fires early, tick_do_update_jiffies64() will just return and do nothing. So what makes jiffies warp?
Unless I'm missing something, this changelog is patently wrong.
Thanks,
tglx
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