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authorStephane Eranian <eranian@google.com>2017-03-15 20:17:13 +0300
committerArnaldo Carvalho de Melo <acme@redhat.com>2017-03-15 23:48:37 +0300
commit88b897a30c525c2eee6e7f16e1e8d0f18830845e (patch)
tree3efca41128bd803b6f55d850c7bef52fd81e4e29 /tools/perf/util/event.c
parent1d585e70905e03e8c19c9aaf523ec246ae6b18a1 (diff)
downloadlinux-88b897a30c525c2eee6e7f16e1e8d0f18830845e.tar.xz
perf tools: 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. Committer note: This problem seems to have been elliminated in the kernel since commit : b18cb64ead40 ("fs/proc: Stop trying to report thread stacks"). Signed-off-by: Stephane Eranian <eranian@google.com> Acked-by: Jiri Olsa <jolsa@redhat.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Namhyung Kim <namhyung@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/20170315135059.GC2177@redhat.com Link: http://lkml.kernel.org/r/1489598233-25586-1-git-send-email-eranian@google.com Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Diffstat (limited to 'tools/perf/util/event.c')
-rw-r--r--tools/perf/util/event.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
index d082cb70445d..33fc2e9c0b0c 100644
--- a/tools/perf/util/event.c
+++ b/tools/perf/util/event.c
@@ -325,8 +325,8 @@ 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) {