linux-kernel - Re: Unable to use tools/perf sched and timechart correctly

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Date:	Sun, 06 Dec 2009 18:41:42 +0800
From:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To:	Török Edwin <edwintorok@...il.com>
CC:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>, Ingo Molnar <mingo@...e.hu>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: Unable to use tools/perf sched and timechart correctly



Török Edwin wrote:
> Hi,
> 
> I installed 2.6.32 and tried its tools/perf.
> I noticed two problems so far, please tell me if I am doing anything
> wrong here:
> 
> 1. 'perf sched replay' segfaults on any recorded workload
> I tested like this:
> $ sudo ./perf sched record
> ^C[ perf record: Woken up 1 times to write data ]                  
> [ perf record: Captured and wrote 0.295 MB perf.data (~12869 samples) ]
> $ sudo perf sched replay
> run measurement overhead: 1258 nsecs                             
> sleep measurement overhead: 55232 nsecs                          
> the run test took 999778 nsecs                                   
> the sleep test took 1055791 nsecs                                
> nr_run_events:        182                                        
> nr_sleep_events:      209                                        
> nr_wakeup_events:     103                                        
> target-less wakeups:  12
> [...]
> task     25 (         icedove-bin:      8757), nr_events: 3
> task     26 (            events/0:        15), nr_events: 3
> ------------------------------------------------------------
> Segmentation fault

You should enable "CONFIG_SCHED_DEBUG", because we use
"/proc/<pid>/sched" file to get the task's cpu usage.

Ingo, I think we do better show the reason about this error,
just like:

---
 tools/perf/builtin-sched.c |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)

diff --git a/tools/perf/builtin-sched.c b/tools/perf/builtin-sched.c
index 26b782f..f823631 100644
--- a/tools/perf/builtin-sched.c
+++ b/tools/perf/builtin-sched.c
@@ -427,7 +427,11 @@ static u64 get_cpu_usage_nsec_self(void)
 
 	sprintf(filename, "/proc/%d/sched", getpid());
 	file = fopen(filename, "r");
-	BUG_ON(!file);
+	if (!file)
+	{
+		printf("You should compile your kernel with CONFIG_SCHED_DEBUG option\n");
+		BUG_ON(1);
+	}
 
 	while ((chars = getline(&line, &len, file)) != -1) {
 		ret = sscanf(line, "se.sum_exec_runtime : %ld.%06ld\n",
-- 
1.6.1.2

Thanks,
Xiao
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