linux-kernel - Re: perf regression: failed to stat syscalls events

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Message-ID: <1277359125.1875.828.camel@laptop>
Date:	Thu, 24 Jun 2010 07:58:45 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: perf regression: failed to stat syscalls events

On Thu, 2010-06-24 at 09:44 +0800, Wu Fengguang wrote:
> On Thu, Jun 24, 2010 at 09:39:15AM +0800, Wu Fengguang wrote:
> > Greetings,
> > 
> > I noticed that
> > 
> >         # perf stat -e syscalls:sys_enter_mmap true
> > 
> > refuse to work on 2.6.35-rc1. The last working kernel is 2.6.34.
> 
> Other events like lock:* or block:* or whatever continue to work.
> So this is a problem specific to syscalls:*.

Does your tree contain:

---
commit a8fb2608053547bc3152ea61a5ec7cdfce5d942c
Author: Steven Rostedt <srostedt@...hat.com>
Date:   Thu Jun 10 14:53:16 2010 -0400

    perf/tracing: Fix regression of perf losing kprobe events
    
    With the addition of the code to shrink the kernel tracepoint
    infrastructure, we lost kprobes being traced by perf. The reason
    is that I tested if the "tp_event->class->perf_probe" existed before
    enabling it. This prevents "ftrace only" events (like the function
    trace events) from being enabled by perf.
    
    Unfortunately, kprobe events do not use perf_probe. This causes
    kprobes to be missed by perf. To fix this, we add the test to
    see if "tp_event->class->reg" exists as well as perf_probe.
    
    Normal trace events have only "perf_probe" but no "reg" function,
    and kprobes and syscalls have the "reg" but no "perf_probe".
    The ftrace unique events do not have either, so this is a valid
    test. If a kprobe or syscall is not to be probed by perf, the
    "reg" function is called anyway, and will return a failure and
    prevent perf from probing it.
    
    Reported-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
    Tested-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
    Acked-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
    Signed-off-by: Steven Rostedt <rostedt@...dmis.org>

diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
index e6f6588..8a2b73f 100644
--- a/kernel/trace/trace_event_perf.c
+++ b/kernel/trace/trace_event_perf.c
@@ -96,7 +96,9 @@ int perf_trace_init(struct perf_event *p_event)
 	mutex_lock(&event_mutex);
 	list_for_each_entry(tp_event, &ftrace_events, list) {
 		if (tp_event->event.type == event_id &&
-		    tp_event->class && tp_event->class->perf_probe &&
+		    tp_event->class &&
+		    (tp_event->class->perf_probe ||
+		     tp_event->class->reg) &&
 		    try_module_get(tp_event->mod)) {
 			ret = perf_trace_event_init(tp_event, p_event);
 			break;

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