linux-kernel - Re: [PATCH] ftrace: Provide trace clock monotonic raw

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Date:	Mon, 4 May 2015 15:10:05 +0000 (UTC)
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	Drew Richardson <drew.richardson@....com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	John Stultz <john.stultz@...aro.org>,
	Wade Cherry <wade.cherry@....com>
Subject: Re: [PATCH] ftrace: Provide trace clock monotonic raw

----- Original Message -----
> Expose the NMI safe accessor to the monotonic raw clock to the
> tracer. The mono clock was added with commit
> 1b3e5c0936046e7e023149ddc8946d21c2ea20eb. Although the monotonic raw
> clock cannot be used to compare time between different machines, it is
> not perterbed by ntp.

perterbed -> perturbed

> 
> Signed-off-by: Drew Richardson <drew.richardson@....com>
>

What is the use-case that justify exposing the "raw fast"
clock that cannot be handled by the "monotonic fast" clock ?

Thanks,

Mathieu

> ---
>  kernel/trace/trace.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 05330494a0df..458031c31a37 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -876,6 +876,7 @@ static struct {
>  	{ trace_clock_jiffies,		"uptime",	0 },
>  	{ trace_clock,			"perf",		1 },
>  	{ ktime_get_mono_fast_ns,	"mono",		1 },
> +	{ ktime_get_raw_fast_ns,	"mono_raw",	1 },
>  	ARCH_TRACE_CLOCKS
>  };
>  
> --
> 2.1.4
> 
> 

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
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