linux-kernel - Re: [PATCH 1/1] rasd: Use perf_evlist_

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Date:	Tue, 14 Oct 2014 08:19:52 -0600
From:	David Ahern <dsahern@...il.com>
To:	Jiri Olsa <jolsa@...hat.com>, Jean Pihet <jean.pihet@...aro.org>
CC:	Borislav Petkov <bp@...en8.de>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Fu Wei <fu.wei@...aro.org>, Robert Richter <rric@...nel.org>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 1/1] rasd: Use perf_evlist__open() instead of open coded

On 10/14/14, 7:56 AM, Jiri Olsa wrote:
> I read the rasd sources and realized we could poke this
> from another angle..  AFAIU the work the rasd does is following:
>     - reads config file and opens configured tracepoints
>     - reads samples comming from those tracepoints and displays/writes
>       this data to the console/file
>     - is there more?
>
> If I'm not missing anything, this is quite usefull/common usage
> pattern which would deserve new perf command.
>
> I can see the analogy with ftrace debugfs interface
>    - choose/enable tracepoints
>    - cat .../tracing/trace-pipe
>
> and there could be '-d' for the command to act as daemon.

Yes, this parallels a new use case on my end. Right now I am running 
perf record ... | perf script. With the tracepoints and filters involved 
it is a LOT of typing - and still collects more than is needed (I don't 
need MMAP events for example, only COMM events). I am leaning towards a 
new perf sub-command but from my scheduling timehist and daemon commands 
I know there is a lot of overhead that goes with that. A perf library 
with a stable API would make this a lot easier. (AFAIK the python 
bindings do not currently support opening events, it is mainly an 
analysis option.)

David

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