[PATCH] perf/powerpc: Cache the DWARF debug info

[Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>]

>From 773a3608a0cd2daf02e244cb9ffbf5bb6a0e724e Mon Sep 17 00:00:00 2001
From: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Date: Tue, 21 Oct 2014 13:20:22 -0500
Subject: [PATCH 1/1] perf/powerpc: Cache DWARF debug info

Cache the DWARF debug info for DSO so we don't have to rebuild it for
each address in the DSO (duh!).

	$ time /tmp/perf.orig report -g > /tmp/report.1

	real	0m1.845s
	user	0m0.963s
	sys	0m0.879s

	$ time /tmp/perf report -g > /tmp/report.2

	real	0m0.089s
	user	0m0.082s
	sys	0m0.006s

	$ diff /tmp/report.1 /tmp/report.2
	$

Reported-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
---
 tools/perf/arch/powerpc/util/skip-callchain-idx.c | 91 ++++++++++++++++++++---
 1 file changed, 82 insertions(+), 9 deletions(-)

diff --git a/tools/perf/arch/powerpc/util/skip-callchain-idx.c b/tools/perf/arch/powerpc/util/skip-callchain-idx.c
index d73ef8b..bfe254d 100644
--- a/tools/perf/arch/powerpc/util/skip-callchain-idx.c
+++ b/tools/perf/arch/powerpc/util/skip-callchain-idx.c
@@ -38,6 +38,63 @@ static const Dwfl_Callbacks offline_callbacks = {
 	.section_address = dwfl_offline_section_address,
 };
 
+struct list_head perf_dwfl_files;
+
+struct perf_dwfl_node {
+	struct list_head node;
+	char *exec_file;
+	Dwfl *dwfl;
+};
+
+static void perf_init_dwfl(void)
+{
+	static int dwfl_inited;
+
+	if (!dwfl_inited) {
+		dwfl_inited = 1;
+		INIT_LIST_HEAD(&perf_dwfl_files);
+	}
+}
+
+static Dwfl *perf_dwfl_find(const char *file_name)
+{
+	struct list_head *pos;
+	struct perf_dwfl_node *node;
+
+	perf_init_dwfl();
+
+	list_for_each(pos, &perf_dwfl_files) {
+		node = list_entry(pos, struct perf_dwfl_node, node);
+		if (!strcmp(node->exec_file, file_name))
+			return node->dwfl;
+	}
+
+	return NULL;
+}
+
+
+/*
+ * Return 1 if were able to cache the DWARF debug info. 0 otherwise.
+ */
+static int perf_dwfl_cache(const char *file_name, Dwfl *dwfl)
+{
+	struct perf_dwfl_node *dwfl_node;
+
+	dwfl_node = malloc(sizeof(struct perf_dwfl_node));
+
+	if (!dwfl_node) {
+		pr_debug("%s(): Unable to alloc memory\n", __func__);
+		return 0;
+	}
+	INIT_LIST_HEAD(&dwfl_node->node);
+	dwfl_node->dwfl = dwfl;
+	dwfl_node->exec_file = strdup(file_name);
+
+	list_add(&dwfl_node->node, &perf_dwfl_files);
+
+	return 1;
+}
+
 
 /*
  * Use the DWARF expression for the Call-frame-address and determine
@@ -155,16 +212,26 @@ static int check_return_addr(const char *exec_file, Dwarf_Addr pc)
 	Dwarf_Addr	start = pc;
 	Dwarf_Addr	end = pc;
 	bool		signalp;
+	int		cached;
 
-	dwfl = dwfl_begin(&offline_callbacks);
+	cached = 1;
+	dwfl = perf_dwfl_find(exec_file);
 	if (!dwfl) {
-		pr_debug("dwfl_begin() failed: %s\n", dwarf_errmsg(-1));
-		return -1;
-	}
-
-	if (dwfl_report_offline(dwfl, "",  exec_file, -1) == NULL) {
-		pr_debug("dwfl_report_offline() failed %s\n", dwarf_errmsg(-1));
-		goto out;
+		dwfl = dwfl_begin(&offline_callbacks);
+		if (!dwfl) {
+			pr_debug("dwfl_begin() failed: %s\n", dwarf_errmsg(-1));
+			return -1;
+		}
+
+		if (dwfl_report_offline(dwfl, "",  exec_file, -1) == NULL) {
+			pr_debug("dwfl_report_offline() failed %s\n",
+							dwarf_errmsg(-1));
+			goto out;
+		}
+		/*
+		 * If we fail to alloc memory, we lose the benefit of caching
+		 */
+		cached = perf_dwfl_cache(exec_file, dwfl);
 	}
 
 	mod = dwfl_addrmodule(dwfl, pc);
@@ -194,7 +261,13 @@ static int check_return_addr(const char *exec_file, Dwarf_Addr pc)
 	rc = check_return_reg(ra_regno, frame);
 
 out:
-	dwfl_end(dwfl);
+	/*
+	 * In the unlikely event that we were unable to cache the debug
+	 * info, release it so we don't leak fds.
+	 */
+	if (!cached)
+		dwfl_end(dwfl);
+
 	return rc;
 }
 
-- 
1.8.4.2