linux-kernel - [PATCH V2] perf/record: make perf_event__synthesize_mmap

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-Id: <1489598233-25586-1-git-send-email-eranian@google.com>
Date:   Wed, 15 Mar 2017 10:17:13 -0700
From:   Stephane Eranian <eranian@...gle.com>
To:     linux-kernel@...r.kernel.org
Cc:     acme@...hat.com, peterz@...radead.org, mingo@...e.hu,
        jolsa@...hat.com, namhyung.kim@...nel.org
Subject: [PATCH V2] perf/record: make perf_event__synthesize_mmap_events() scale

This patch significantly improves the execution time of
perf_event__synthesize_mmap_events() when running perf record
on systems where processes have lots of threads. It just happens
that cat /proc/pid/maps support uses a O(N^2) algorithm to generate
each map line in the maps file.  If you have 1000 threads, then you have
necessarily 1000 stacks.  For each vma, you need to check if it corresponds
to a thread's stack.  With a large number of threads, this can take a very long time. I have seen latencies >> 10mn.

As of today, perf does not use the fact that a mapping is a stack,
therefore we can work around the issue by using /proc/pid/tasks/pid/maps.
This entry does not try to map a vma to stack and is thus much
faster with no loss of functonality.

The proc-map-timeout logic is kept in case users still want some upper limit.

In V2, we fix the file path from /proc/pid/tasks/pid/maps to
actual /proc/pid/task/pid/maps, tasks -> task.
Thanks Arnaldo for catching this.

Signed-off-by: Stephane Eranian <eranian@...gle.com>

---
 tools/perf/util/event.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
index 4ea7ce7..b137566 100644
--- a/tools/perf/util/event.c
+++ b/tools/perf/util/event.c
@@ -255,8 +255,8 @@ int perf_event__synthesize_mmap_events(struct perf_tool *tool,
 	if (machine__is_default_guest(machine))
 		return 0;

-	snprintf(filename, sizeof(filename), "%s/proc/%d/maps",
-		 machine->root_dir, pid);
+	snprintf(filename, sizeof(filename), "%s/proc/%d/task/%d/maps",
+		 machine->root_dir, pid, pid);

 	fp = fopen(filename, "r");
 	if (fp == NULL) {
-- 
2.5.0