linux-kernel - Re: [PATCH v2] rtc: Add tracepoints for RTC system

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Date:   Wed, 13 Dec 2017 11:46:29 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Mark Brown <broonie@...nel.org>
Cc:     Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
        Arnd Bergmann <arnd@...db.de>,
        Baolin Wang <baolin.wang@...aro.org>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Ingo Molnar <mingo@...hat.com>, linux-rtc@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] rtc: Add tracepoints for RTC system

On Wed, 13 Dec 2017 12:16:03 +0000
Mark Brown <broonie@...nel.org> wrote:

> On Wed, Dec 13, 2017 at 12:04:26PM +0100, Alexandre Belloni wrote:
> 
> > Also, I think we could try having only the time64_t in the ring buffer.
> > Maybe I'm wrong but I think tools reading that buffer can do the
> > conversion themselves. Maybe I don't understand correctly how
> > tracepoints work and this doesn't make sense, tell me.  
> 
> Tools reading the buffer can do the conversion themselves but it's also
> useful for users to just view the log directly via tracing/trace
> sometimes.  OTOH the whole point is to be low overhead so...

Ideally, we want TP_fast_assign() do as little as possible, and put all
the work in TP_printk() as the printk happens on read of the trace
buffer and TP_fast_assign() happens at the tracepoint invocation.

-- Steve