Re: [PATCH-v2] tracing: Fix wraparound problems in "uptime" tracer

[Tony Luck]

On Thu, Jul 17, 2014 at 7:08 PM, Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
>> Do we really need to convert to nanoseconds? Couldn't we just return
>> jiffies:
>
> Sure, and we can make it a "counter". That is, the counters don't hide
> 1000 counts on output.

Can you explain that a bit more ... how do we mark it as a "counter"?

>> u64 notrace trace_clock_jiffies(void)
>> {
>>        return jiffies_64 - INITIAL_JIFFIES;
>> }

Hmm it seems that we make it hard for applications to see what HZ
value the kernel is actually using. All user-facing interfaces should
convert to USER_HZ (100).  So we should say:

u64 notrace trace_clock_jiffies(void)
{
        return jiffies_64_to_clock_t(jiffies_64 - INITIAL_JIFFIES);
}

Do we need to change anything in Documentation/trace/ftrace.txt?

Currently it says:

          uptime: This uses the jiffies counter and the time stamp
                  is relative to the time since boot up.

-Tony
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