linux-kernel - Re: [PATCH] stm class: Document the stm

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Message-ID: <CAAfSe-unLWMp_bESETbD5U_NoaCgo+RvuKGTP3wwLdXCZWUi=A@mail.gmail.com>
Date:   Tue, 21 Mar 2017 13:57:59 +0800
From:   Chunyan Zhang <zhang.lyra@...il.com>
To:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc:     Chunyan Zhang <chunyan.zhang@...eadtrum.com>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        nicolas.guion@...com
Subject: Re: [PATCH] stm class: Document the stm_ftrace

On 20 March 2017 at 19:09, Alexander Shishkin
<alexander.shishkin@...ux.intel.com> wrote:
> Chunyan Zhang <zhang.lyra@...il.com> writes:
>
>> Hi Alex,
>>
>> On 20 March 2017 at 16:49, Alexander Shishkin
>> <alexander.shishkin@...ux.intel.com> wrote:
>>> Hi Chunyan,
>>>
>>> A couple of clarifications: iirc this applies to the function tracer
>>> of ftrace, right? Does it make sense to mention that? Also, are you
>>
>> Right, only applies to the function tracer currently (actually only
>> function address and parent function address of Function tracer is
>> recorded into STM, I mean it doesn't include like "pid" "task name"
>> "cpu-id" these information right now). It makes sense to mention
>> function tracer, I will address that.
>
> Thanks!
>
>>> planning to support other ftrace payloads like trace_printk()s?
>>
>> No plan so far, but I think I can consider to do that, it depends on
>> how many people think that are helpful.
>> What do you think?
>
> Well, I myself almost never use function tracer, but I do use
> tracepoints/trace_printk()s. I'm *guessing* that everybody who's

In fact I had implemented exporting tracepoints to STM and tried
upstreaming that, but Steven Rostedt and Ingo expressed their worries
on that would introduce a considerable impact on Ftrace fast path
since a tracepoint basically was a string which was too long to be
written to STM with some acceptable impact on fast path, so I stopped
upstreaming that feature.

Thanks,
Chunyan

> subsystem implement tracepoints will be interested in those.
>
> I confess that I haven't yet looked at the code properly, so I'm a don't
> have a picture of what it will take to implement these.
>
> Regards,
> --
> Alex