linux-kernel - [RFC PATCH] Perf: Fix an issue where perf report fails to show the proper percentage

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Message-ID: <20120203170113.5190.25558.stgit@localhost6.localdomain6>
Date:	Fri, 03 Feb 2012 22:31:13 +0530
From:	"Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:	acme@...hat.com, mingo@...e.hu, linux-kernel@...r.kernel.org
Cc:	robert.richter@....com, ananth@...ibm.com,
	srikar@...ux.vnet.ibm.com
Subject: [RFC PATCH] Perf: Fix an issue where perf report fails to show the
	proper percentage

This patch fixes an issue where perf report shows nan% for certain
perf.data files. The below is from a report for a do_fork probe:

   -nan%           sshd  [kernel.kallsyms]  [k] do_fork
   -nan%    packagekitd  [kernel.kallsyms]  [k] do_fork
   -nan%    dbus-daemon  [kernel.kallsyms]  [k] do_fork
   -nan%           bash  [kernel.kallsyms]  [k] do_fork

A git bisect shows commit f3bda2c as the cause. However, looking back through
the git history, I saw commit 640c03c which seems to have removed the
required initialization for perf_sample->period. The problem only started
showing after commit f3bda2c. The below patch re-introduces the
initialization and it fixes the problem for me.

With the below patch, for the same perf.data:

  73.08%             bash  [kernel.kallsyms]  [k] do_fork
   8.97%      11-dhclient  [kernel.kallsyms]  [k] do_fork
   6.41%             sshd  [kernel.kallsyms]  [k] do_fork
   3.85%        20-chrony  [kernel.kallsyms]  [k] do_fork
   2.56%         sendmail  [kernel.kallsyms]  [k] do_fork

This patch applies over current linux-tip commit 9949284.

Signed-off-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
---
 tools/perf/util/evsel.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index dcfefab..9a11f9e 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -463,6 +463,7 @@ int perf_event__parse_sample(const union perf_event *event, u64 type,
 	memset(data, 0, sizeof(*data));
 	data->cpu = data->pid = data->tid = -1;
 	data->stream_id = data->id = data->time = -1ULL;
+	data->period = 1;
 
 	if (event->header.type != PERF_RECORD_SAMPLE) {
 		if (!sample_id_all)

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