linux-kernel - Re: [PATCH V9 1/6] perf,tools: introduce generic FEAT for CPU attributes

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Date:	Thu, 10 Sep 2015 12:35:15 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	kan.liang@...el.com
Cc:	Jiri Olsa <jolsa@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>, luto@...nel.org,
	Ingo Molnar <mingo@...nel.org>,
	Stephane Eranian <eranian@...gle.com>, ak@...ux.intel.com,
	mark.rutland@....com, adrian.hunter@...el.com,
	Namhyung Kim <namhyung@...nel.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH V9 1/6] perf,tools: introduce generic FEAT for CPU
 attributes

Em Thu, Sep 10, 2015 at 10:58:38AM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Tue, Sep 08, 2015 at 03:32:44PM -0400, kan.liang@...el.com escreveu:
> > This patch introduces generic FEAT for CPU attributes. For the patch
> > set, we only need cpu max frequency. But it can be easily extented to
> > support more other CPU attributes.
> > The cpu max frequency is from the first online cpu.
 
> Ok, but don't we have to do error handling? i.e. you are returning 0 for
> any error in trying to read the cpu max freq, shouldn't we bail out
> somewhere?
 
> And please move this get_cpu_max_freq() thing out of the cpumap.[ch]
> files, it is not even a need completely specific to perf tooling, there
> must be somewhere in tools/lib/api/ (kernel APIs) where this fits, no?

So, I've updated my perf/env branch with routines to do that, that uses
infrastructure to read files from virtual dirs that was there plus a few
I just introduced, in the same vein, I will update your patches to use
them and put there as well, for your consideration.

The HEAD there is the one below:

- Arnaldo

commit 2bc1fae4ed8a842f52dc374449d37c3ec1fa1986
Author: Arnaldo Carvalho de Melo <acme@...hat.com>
Date:   Thu Sep 10 12:20:14 2015 -0300

    tools lib cpu: Introduce cpu.[ch] to read sysfs cpu related information
    
    E.g.:
    
     $ ./cpu__get_max_freq
     3200000
    
    It does that, as Kan's patch does, by looking at these files:
    
      $ cat /sys/devices/system/cpu/online
      0-3
      $ ./sysfs__read_ull
      devices/system/cpu/cpu0/cpufreq/cpuinfo_max_freq
      /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_max_freq=3200000
      $
    
    I.e. find out the first online CPU, then read its cpufreq info.
    
    But do it in tools/lib/api/, so that other tools living code can use
    it, not just perf.
    
    Based-on-a-patch-by: Kan Liang <kan.liang@...el.com>
    Cc: Adrian Hunter <adrian.hunter@...el.com>
    Cc: Borislav Petkov <bp@...e.de>
    Cc: David Ahern <dsahern@...il.com>
    Cc: Frederic Weisbecker <fweisbec@...il.com>
    Cc: Jiri Olsa <jolsa@...hat.com>
    Cc: Namhyung Kim <namhyung@...nel.org>
    Cc: Stephane Eranian <eranian@...gle.com>
    Link: http://lkml.kernel.org/n/tip-915v4cvxqplaub8qco66b9mv@git.kernel.org
    Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>

diff --git a/tools/lib/api/Build b/tools/lib/api/Build
index 3653965cf481..e8b8a23b9bf4 100644
--- a/tools/lib/api/Build
+++ b/tools/lib/api/Build
@@ -1,2 +1,3 @@
 libapi-y += fd/
 libapi-y += fs/
+libapi-y += cpu.o
diff --git a/tools/lib/api/cpu.c b/tools/lib/api/cpu.c
new file mode 100644
index 000000000000..8c6489356e3a
--- /dev/null
+++ b/tools/lib/api/cpu.c
@@ -0,0 +1,18 @@
+#include <stdio.h>
+
+#include "cpu.h"
+#include "fs/fs.h"
+
+int cpu__get_max_freq(unsigned long long *freq)
+{
+	char entry[PATH_MAX];
+	int cpu;
+
+	if (sysfs__read_int("devices/system/cpu/online", &cpu) < 0)
+		return -1;
+
+	snprintf(entry, sizeof(entry),
+		 "devices/system/cpu/cpu%d/cpufreq/cpuinfo_max_freq", cpu);
+
+	return sysfs__read_ull(entry, freq);
+}
diff --git a/tools/lib/api/cpu.h b/tools/lib/api/cpu.h
new file mode 100644
index 000000000000..81e9d3955961
--- /dev/null
+++ b/tools/lib/api/cpu.h
@@ -0,0 +1,6 @@
+#ifndef __API_CPU__
+#define __API_CPU__
+
+int cpu__get_max_freq(unsigned long long *freq);
+
+#endif /* __API_CPU__ */
--
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