Re: [PATCH] tracing: Export key trace event symbols

[David Ahern <dsahern@gmail.com>]

On 4/22/15 8:47 AM, Arnaldo Carvalho de Melo wrote:
> Em Wed, Apr 22, 2015 at 08:53:14AM -0400, Steven Rostedt escreveu:
>> >On Tue, 21 Apr 2015 21:24:51 -0500
>> >Ron Rechenmacher<ron@fnal.gov>  wrote:
>>> > >I've looked at the above reference briefly and it appears that user-space
>>> > >would be mmapping the buffer read-only. Is that correct?
>> >
>> >Correct, but I'm sure we could still add something (if it doesn't
>> >already exist) to have userspace write into the buffer. Ftrace has that
>> >with the trace_marker file.
> There is something in the works, I guess Pawell Moll (sp) was working on it, and
> David Ahern (CCed) should know, David?
>

I played around with generating perf events in userspace with the 
intention of having the userspace events get merged with kernel events 
during the processing stage, but I did not take it to the point of 
integrating into perf. This was around October 2013. I got distracted 
with other topics and have not come back to it.

Pawel has a patch that allows userspace to inject events into the stream 
via ioctl calls.

Stephane also injects events for JIT.

One of the key requirements is a common time basis (e.g., 
CLOCK_MONOTONIC or PERF_CLOCK) to be able to merge the events properly. 
I have a kernel module that exports perf_clock to userspace via 
clock_gettime; the 4.1 kernel should have the code that allows the clock 
id to be specified providing a solution to this problem.

David