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Subject[RFC][PATCH] Fix inhert with perf record --pid

A gently tested RFC patch...
---


From 38554891fc41082b767f24ce3293658f7329a691 Mon Sep 17 00:00:00 2001
From: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Date: Fri, 8 Nov 2013 17:14:06 -0800
Subject: [PATCH] Fix inhert with perf record --pid

If a target process is identified by its pid:

perf record --pid 1234

perf record does not follow any _newly_ created children of the
process. perf_evlist__config() clears the ->inherit flag.

if (evlist->cpus->map[0] < 0)
opts->no_inherit = true;

It can be fixed and descendants can be followed, by this change
below, but is this behavior by design ?

We do follow the children if the same process is started by perf:

perf record ./a.out

This was reported by Maynard Johnson <mpjohn@us.ibm.com>

On a related note, perf_target__validate() has this:

/* CPU and PID are mutually exclusive */
if (target->tid && target->cpu_list) {
target->cpu_list = NULL;
if (ret == PERF_ERRNO_TARGET__SUCCESS)
ret = PERF_ERRNO_TARGET__PID_OVERRIDE_CPU;
}

Again, its not clear why pid and cpu are exclusive in this case:

perf record --pid 1234 -C 0,1,2

The system call allows the both pid and cpu to be specified.

Looking at commit, I see that this check was pulled in from builtin-top.c.

commit 4bd0f2d2c0cf14de9c84c2fe689120c6b0f667c8
Author: Namhyung Kim <namhyung.kim@lge.com>
Date: Thu Apr 26 14:15:18 2012 +0900

Does that check apply to 'perf record' or only 'perf top' ?

Appreciate any comments.

---
tools/perf/util/evlist.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
index e584cd3..c81d01a 100644
--- a/tools/perf/util/evlist.c
+++ b/tools/perf/util/evlist.c
@@ -742,7 +742,7 @@ int perf_evlist__create_maps(struct perf_evlist *evlist,
return -1;

if (perf_target__has_task(target))
- evlist->cpus = cpu_map__dummy_new();
+ evlist->cpus = cpu_map__new(target->cpu_list);
else if (!perf_target__has_cpu(target) && !target->uses_mmap)
evlist->cpus = cpu_map__dummy_new();
else
--
1.7.1


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