linux-kernel - Re: [PATCH v4 3/3] tracing: Histogram for missed timer offsets

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Date:   Fri, 2 Sep 2016 18:11:39 +0530
From:   Binoy Jayan <binoy.jayan@...aro.org>
To:     Masami Hiramatsu <masami.hiramatsu@...aro.org>
Cc:     "Steven Rostedt (Red Hat)" <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Daniel Wagner <daniel.wagner@...-carit.de>,
        Arnd Bergmann <arnd@...db.de>,
        Linux kernel mailing list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 3/3] tracing: Histogram for missed timer offsets

On 30 August 2016 at 16:20, Masami Hiramatsu
<masami.hiramatsu@...aro.org> wrote:
> Hi Binoy,
>>
>> +static inline void trace_latency_hrtimer_mark_ts(struct hrtimer *timer,
>> +                                        struct hrtimer_clock_base *new_base,
>> +                                        ktime_t tim)
>> +{
>> +#if defined(CONFIG_PREEMPT_TRACER) || defined(CONFIG_IRQSOFF_TRACER)
>> +       if (trace_latency_hrtimer_interrupt_enabled()) {
>
> You would better use unlikely() here.
>
>> +               ktime_t now = new_base->get_time();
>> +
>> +               if (ktime_to_ns(tim) < ktime_to_ns(now))
>
> Wouldn't we need to consider the case of wrap around?
>
>> +                       timer->praecox = now;
>> +               else
>> +                       timer->praecox = ktime_set(0, 0);
>> +       }
>> +#endif
>> +}

Hi Masami,

I always see these values to be relative and not absolute time. I
found 'praecox' to be always zero during test.
What do you think.

Binoy