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

From: David Ahern
Date: Wed Apr 22 2015 - 11:36:30 EST


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@xxxxxxxx> 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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