linux-kernel - Re: [PATCH] tracing: Export key trace event symbols

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Date:	Wed, 22 Apr 2015 09:36:20 -0600
From:	David Ahern <dsahern@...il.com>
To:	Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>
CC:	Ron Rechenmacher <ron@...l.gov>,
	Christoph Hellwig <hch@...radead.org>,
	linux-kernel@...r.kernel.org,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH] tracing: Export key trace event symbols

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@...l.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
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