linux-kernel - [PATCH] perf tools: Unset perf_event_attr::freq when period term is set

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Date:	Sat, 8 Aug 2015 19:12:10 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	kan.liang@...el.com, jolsa@...nel.org, namhyung@...nel.org,
	ak@...ux.intel.com, linux-kernel@...r.kernel.org
Subject: [PATCH] perf tools: Unset perf_event_attr::freq when period term is
 set

On Fri, Aug 07, 2015 at 12:38:43PM -0300, Arnaldo Carvalho de Melo wrote:
> 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...

my kungu foo found there was actually another issue ;-)

we did not clear up attr->freq bit.. so the sample_period
was handled as sample_freq value.. please check the patch
below

anyfoo, now period setup can raise sky high (which is correct)
and once it meets the God it shows:

[jolsa@...va perf]$ ./perf record -e 'cpu/cpu-cycles,call-graph=fp,time,period=1000000000000000000000000/' ls
event syntax error: '..time,period=1000000000000000000000000/'
                                  \___ parser error

I'll check if we could add some default error message when value
crosses the type maximum.. which now falls to parser error

jirka


---
We need to unset 'perf_event_attr::freq' bit (default 1) when
'period' term is specified within event definition like:

  -e 'cpu/cpu-cycles,call-graph=fp,time,period=100000'

otherwise it will handle the period value as frequency
(and fail if it crossed the maximum allowed frequency value).

Signed-off-by: Jiri Olsa <jolsa@...nel.org>
Link: http://lkml.kernel.org/n/tip-7f3gjwbekakhyxr47wvin4zb@git.kernel.org
---
diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index d902cad4ce10..4c779d23b1d7 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -623,6 +623,7 @@ static void apply_config_terms(struct perf_evsel *evsel,
 		switch (term->type) {
 		case PERF_EVSEL__CONFIG_TERM_PERIOD:
 			attr->sample_period = term->val.period;
+			attr->freq = 0;
 			break;
 		case PERF_EVSEL__CONFIG_TERM_TIME:
 			if (term->val.time)
--
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