linux-kernel - [PATCH 01/18] perf evlist: Fixup brown paper bag on "hint" for --mmap-pages cmdline arg

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Date:	Tue, 16 Dec 2014 13:57:03 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	linux-kernel@...r.kernel.org,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Borislav Petkov <bp@...e.de>, David Ahern <dsahern@...il.com>,
	Don Zickus <dzickus@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Olsa <jolsa@...hat.com>, Mike Galbraith <efault@....de>,
	Namhyung Kim <namhyung@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Stephane Eranian <eranian@...gle.com>
Subject: [PATCH 01/18] perf evlist: Fixup brown paper bag on "hint" for --mmap-pages cmdline arg

From: Arnaldo Carvalho de Melo <acme@...hat.com>

When failing due to asking for a number of mmap pages that is more than
the max, it was suggesting that an even bigger number of mmap pages
should be specified, doh, au contraire!

Before:

  [acme@...andy linux]$ trace -m 128 usleep 1
  Error:	Operation not permitted.
  Hint:	Check /proc/sys/kernel/perf_event_mlock_kb (516 kB) setting.
  Hint:	Tried using 516 kB.
  Hint:	Try using a bigger -m/--mmap-pages value.
  [acme@...andy linux]$

After:

  [acme@...andy linux]$ trace -m 128 usleep 1
  Error:	Operation not permitted.
  Hint:	Check /proc/sys/kernel/perf_event_mlock_kb (516 kB) setting.
  Hint:	Tried using 516 kB.
  Hint:	Try using a smaller -m/--mmap-pages value.
  [acme@...andy linux]$

And to (really) clarify what happens above, when what the user requests
is <= max and even then it fails, a changeset is being made to tell that
this is a per user limit, not per process (in the above example there
was another 'perf trace' running for this user, which was using all the
pages it could use).

Cc: Adrian Hunter <adrian.hunter@...el.com>
Cc: Borislav Petkov <bp@...e.de>
Cc: David Ahern <dsahern@...il.com>
Cc: Don Zickus <dzickus@...hat.com>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Mike Galbraith <efault@....de>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Paul Mackerras <paulus@...ba.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Stephane Eranian <eranian@...gle.com>
Link: http://lkml.kernel.org/n/tip-8qope8lxb898narnq5kmu2gf@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
---
 tools/perf/util/evlist.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
index bb5dfc5d1e75..de7515dd683a 100644
--- a/tools/perf/util/evlist.c
+++ b/tools/perf/util/evlist.c
@@ -1495,7 +1495,7 @@ int perf_evlist__strerror_mmap(struct perf_evlist *evlist, int err, char *buf, s
 		scnprintf(buf, size, "Error:\t%s.\n"
 				     "Hint:\tCheck /proc/sys/kernel/perf_event_mlock_kb (%d kB) setting.\n"
 				     "Hint:\tTried using %zd kB.\n"
-				     "Hint:\tTry using a bigger -m/--mmap-pages value.",
+				     "Hint:\tTry using a smaller -m/--mmap-pages value.",
 				     emsg, value, evlist->mmap_len / 1024);
 		break;
 	default:
-- 
1.9.3

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