linux-kernel - [tip:perf/urgent] perf evlist: Do not use hard coded value for a mmap

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Message-ID: <tip-2f6mtm8xu3wo5lhkql6jdblh@git.kernel.org>
Date:	Wed, 17 Dec 2014 22:29:15 -0800
From:	tip-bot for Arnaldo Carvalho de Melo <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	dzickus@...hat.com, namhyung@...nel.org, paulus@...ba.org,
	efault@....de, fweisbec@...il.com, adrian.hunter@...el.com,
	tglx@...utronix.de, mingo@...nel.org, acme@...hat.com,
	peterz@...radead.org, jolsa@...hat.com,
	linux-kernel@...r.kernel.org, eranian@...gle.com, bp@...e.de,
	hpa@...or.com, dsahern@...il.com
Subject: [tip:perf/urgent] perf evlist:
  Do not use hard coded value for a mmap_pages default

Commit-ID:  8185e881f9fd9a2fa01f9d45616f8587f485f2a6
Gitweb:     http://git.kernel.org/tip/8185e881f9fd9a2fa01f9d45616f8587f485f2a6
Author:     Arnaldo Carvalho de Melo <acme@...hat.com>
AuthorDate: Fri, 12 Dec 2014 17:46:45 -0300
Committer:  Arnaldo Carvalho de Melo <acme@...hat.com>
CommitDate: Tue, 16 Dec 2014 13:38:26 -0300

perf evlist: Do not use hard coded value for a mmap_pages default

So far what is in there by default is what we were using: 512KB + the
control page, but the admin may change that, and if it does to a smaller
value, all calls to tooling for non root users start failing, requiring
that the user manually set --mmap_pages/-m.

Use instead what is in /proc/sys/kernel/perf_event_mlock_kb.

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-2f6mtm8xu3wo5lhkql6jdblh@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
---
 tools/perf/util/evlist.c | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
index 7847f38..ac80868 100644
--- a/tools/perf/util/evlist.c
+++ b/tools/perf/util/evlist.c
@@ -893,10 +893,22 @@ out_unmap:
 
 static size_t perf_evlist__mmap_size(unsigned long pages)
 {
-	/* 512 kiB: default amount of unprivileged mlocked memory */
-	if (pages == UINT_MAX)
-		pages = (512 * 1024) / page_size;
-	else if (!is_power_of_2(pages))
+	if (pages == UINT_MAX) {
+		int max;
+
+		if (sysctl__read_int("kernel/perf_event_mlock_kb", &max) < 0) {
+			/*
+			 * Pick a once upon a time good value, i.e. things look
+			 * strange since we can't read a sysctl value, but lets not
+			 * die yet...
+			 */
+			max = 512;
+		} else {
+			max -= (page_size / 1024);
+		}
+
+		pages = (max * 1024) / page_size;
+	} else if (!is_power_of_2(pages))
 		return 0;
 
 	return (pages + 1) * page_size;
--
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