linux-kernel - Re: perf/ftrace: does PERF_EVENT_IOC_SET

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Message-ID: <55774585.7030000@gmail.com>
Date:	Tue, 09 Jun 2015 13:59:01 -0600
From:	David Ahern <dsahern@...il.com>
To:	Vince Weaver <vincent.weaver@...ne.edu>
CC:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Stephane Eranian <eranian@...il.com>,
	Jiri Olsa <jolsa@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: perf/ftrace: does PERF_EVENT_IOC_SET_FILTER serve any purpose?

On 6/9/15 2:02 PM, Vince Weaver wrote:
> # ls/sys/kernel/debug/tracing/events/irq/irq_handler_entry/
> enable	filter	format	id  trigger
>
> # perf list
> ....
>    [ Tracepoints not available: No such file or directory ]
>
> strace shows
> statfs("/sys/kernel/debug/tracing/events", {f_type=0x74726163,
> f_bsize=4096, f_blocks=0, f_bfree=0, f_bavail=0, f_files=0, f_ffree=0,
> f_fsid={0, 0}, f_namelen=255, f_frsize=4096}) = 0
>
> so I have no idea what's going wrong here.

Check Steven's email; probably the issue.

>
>
> Anyway, on a related question, I see for the event that you use
> 	--filter irq==28
> How do I find out the valid filters for each event?  Do I have to parse
> the "format" file under
> 	/sys/kernel/debug/tracing/events/*/* ?

Yes. And *very important* don't use the print fmt names, but the field 
names. Often they are the same but when they differ it can be maddening.
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