Re: [PATCH] stm class: Document the stm_ftrace

[Alexander Shishkin]

On 21 March 2017 at 07:57, Chunyan Zhang <zhang.lyra@xxxxxxxxx> wrote:
> On 20 March 2017 at 19:09, Alexander Shishkin
> <alexander.shishkin@xxxxxxxxxxxxxxx> wrote:
>> Chunyan Zhang <zhang.lyra@xxxxxxxxx> writes:
>>
>>> Hi Alex,
>>>
>>> On 20 March 2017 at 16:49, Alexander Shishkin
>>> <alexander.shishkin@xxxxxxxxxxxxxxx> 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.

Did we ever consider writing a string pointer (or even on offset into
the corresponding section, to avoid KASLR fun) instead of the actual
string? This would require a kernel binary on the decoding end,
though.

Regards,
--
Alex