linux-kernel - [PATCH 4/5] perf record: Allow to specify max stack depth of fp callchain

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Date:   Tue, 31 May 2022 23:58:45 -0700
From:   Namhyung Kim <namhyung@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ian Rogers <irogers@...gle.com>,
        linux-perf-users@...r.kernel.org, Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Davidlohr Bueso <dave@...olabs.net>
Subject: [PATCH 4/5] perf record: Allow to specify max stack depth of fp callchain

Currently it has no interface to specify the max stack depth for perf
record.  Extend the command line parameter to accept a number after
'fp' to specify the depth like '--call-graph fp,32'.

Signed-off-by: Namhyung Kim <namhyung@...nel.org>
---
 tools/perf/Documentation/perf-record.txt |  5 +++++
 tools/perf/util/callchain.c              | 18 ++++++++++++------
 2 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt
index b4e9ef7edfef..d2759e2ccf9e 100644
--- a/tools/perf/Documentation/perf-record.txt
+++ b/tools/perf/Documentation/perf-record.txt
@@ -275,6 +275,11 @@ OPTIONS
 	User can change the size by passing the size after comma like
 	"--call-graph dwarf,4096".
 
+	When "fp" recording is used, perf tries to save stack enties
+	up to the number specified in sysctl.kernel.perf_event_max_stack
+	by default.  User can change the number by passing it after comma
+	like "--call-graph fp,32".
+
 -q::
 --quiet::
 	Don't print any message, useful for scripting.
diff --git a/tools/perf/util/callchain.c b/tools/perf/util/callchain.c
index 5c27a4b2e7a7..7e663673f79f 100644
--- a/tools/perf/util/callchain.c
+++ b/tools/perf/util/callchain.c
@@ -31,6 +31,7 @@
 #include "callchain.h"
 #include "branch.h"
 #include "symbol.h"
+#include "util.h"
 #include "../perf.h"
 
 #define CALLCHAIN_PARAM_DEFAULT			\
@@ -266,12 +267,17 @@ int parse_callchain_record(const char *arg, struct callchain_param *param)
 	do {
 		/* Framepointer style */
 		if (!strncmp(name, "fp", sizeof("fp"))) {
-			if (!strtok_r(NULL, ",", &saveptr)) {
-				param->record_mode = CALLCHAIN_FP;
-				ret = 0;
-			} else
-				pr_err("callchain: No more arguments "
-				       "needed for --call-graph fp\n");
+			ret = 0;
+			param->record_mode = CALLCHAIN_FP;
+
+			tok = strtok_r(NULL, ",", &saveptr);
+			if (tok) {
+				unsigned long size;
+
+				size = strtoul(tok, &name, 0);
+				if (size < (unsigned) sysctl__max_stack())
+					param->max_stack = size;
+			}
 			break;
 
 		/* Dwarf style */
-- 
2.36.1.255.ge46751e96f-goog