linux-kernel - [RFC][PATCH] Fix inhert with perf record --pid

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Date:	Fri, 8 Nov 2013 18:02:33 -0800
From:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
To:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Jiri Olsa <jolsa@...hat.com>, a.p.zijlstra@...llo.nl,
	namhyung@...nel.org
Cc:	linux-kernel@...r.kernel.org, Maynard Johnson <mpjohn@...ibm.com>
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@...ux.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@...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@....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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