linux-kernel - Re: [PATCH RFC V9 2/3] perf,tools: per-event callgraph support

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Date:	Fri, 7 Aug 2015 12:38:43 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	kan.liang@...el.com
Cc:	jolsa@...nel.org, namhyung@...nel.org, ak@...ux.intel.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC V9 2/3] perf,tools: per-event callgraph support

Em Thu, Aug 06, 2015 at 03:44:53PM -0400, kan.liang@...el.com escreveu:
> From: Kan Liang <kan.liang@...el.com>
> Here are some examples and test results.
> 
> 1. Comparing the elapsed time and perf.data size from "kernbench -M -H".
> 
>  The test command for FULL callgraph and time support.
>    "perf record -e
>    '{cpu/cpu-cycles,period=100000/,cpu/instructions,period=20000/p}'
>    --call-graph fp --time"

Jiri, while testing this I noticed that the message for EINVAL when
using the cpu// syntax (per-event settings) is cryptic:

  [root@zoo ~]# perf record -e 'cpu/cpu-cycles,call-graph=fp,time,period=100000/p' ls
  Error:
  The sys_perf_event_open() syscall returned with 22 (Invalid argument) for event (cpu/cpu-cycles,call-graph=fp,time,period=100000/p).
  /bin/dmesg may provide additional information.
  No CONFIG_PERF_EVENTS=y kernel support configured?

Whereas if we use -F, it is much, much clearer, telling the user exactly
what is failing and what needs to be done to make it work:

  [root@zoo ~]# perf record -F 100000 -e cpu/cpu-cycles/ usleep 1
  Maximum frequency rate (25000) reached.
  Please use -F freq option with lower value or consider
  tweaking /proc/sys/kernel/perf_event_max_sample_rate.
  [root@zoo ~]# 

Hope this is something easy to wire up, given your event parsing kung foo
skillz...

;-)

- Arnaldo
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