linux-kernel - Re: Ftrace Data Export

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Date:   Wed, 17 May 2017 20:45:22 +0800
From:   Chunyan Zhang <zhang.chunyan@...aro.org>
To:     Felipe Balbi <felipe.balbi@...ux.intel.com>
Cc:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>
Subject: Re: Ftrace Data Export

Hi Felipe,

On 17 May 2017 at 16:08, Felipe Balbi <felipe.balbi@...ux.intel.com> wrote:
>
> Hi Chunyan,
>
> When you wrote your patchset to provide ftrace exports, why did you
> choose to export only function trace? Why not tracepoints,

In fact, I tried submitting patches[1] to do exporting tracepoint to
STM, but Ingo and Steven commented that would introduce certain amount
of overhead, and that was not acceptable. I also used
'benchmark_event' to see the additional overhead caused by printing
tracepoint message to STM.  I cannot remember the exact data though,
the increased time consuming indeed was non-ignorable.

So at the end I gave up that idea, and later on switched to the way of
implementation you see in the kernel now.

> function_graph, hwlat, irqsoff and all the other possibilities?

I haven't thought about these clear enough :)
Any suggestion?

Thanks,
Chunyan

[1] https://lkml.org/lkml/2015/7/7/230

>
> Is there an underlying reason why you chose to export only function
> trace?
>
> Thanks
>
> --
> balbi