[PATCH] tracing/fastboot: document the need of initcall_debug

[PATCH] tracing/fastboot: document the need of initcall_debug

[Li Zefan]

To use boot tracer, one should pass initcall_debug as well as
ftrace=initcall to the command line.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
---
 kernel/trace/Kconfig |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index f7d9a4e..860c712 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -226,13 +226,13 @@ config BOOT_TRACER
 	  the timings of the initcalls and traces key events and the identity
 	  of tasks that can cause boot delays, such as context-switches.
 
-	  Its aim is to be parsed by the /scripts/bootgraph.pl tool to
+	  Its aim is to be parsed by the scripts/bootgraph.pl tool to
 	  produce pretty graphics about boot inefficiencies, giving a visual
 	  representation of the delays during initcalls - but the raw
 	  /debug/tracing/trace text output is readable too.
 
-	  You must pass in ftrace=initcall to the kernel command line
-	  to enable this on bootup.
+	  You must pass in initcall_debug and ftrace=initcall to the kernel
+	  command line to enable this on bootup.
 
 config TRACE_BRANCH_PROFILING
 	bool
-- 
1.5.4.rc3

Re: [PATCH] tracing/fastboot: document the need of initcall_debug

[Ingo Molnar]

* Li Zefan <lizf@cn.fujitsu.com> wrote:

> To use boot tracer, one should pass initcall_debug as well as
> ftrace=initcall to the command line.

I think both should be auto-enabled if BOOT_TRACER is enabled, for 
ease of use - agreed?

	Ingo

Re: [PATCH] tracing/fastboot: document the need of initcall_debug

[Li Zefan]

Ingo Molnar wrote:
> * Li Zefan <lizf@cn.fujitsu.com> wrote:
> 
>> To use boot tracer, one should pass initcall_debug as well as
>> ftrace=initcall to the command line.
> 
> I think both should be auto-enabled if BOOT_TRACER is enabled, for 
> ease of use - agreed?
> 

If both are auto-enabled, we'll always do boot tracing. But we want
BOOT_TRACER to be enabled and only enable boot tracing when it's needed.

But maybe we can make ftrace=initcall implies initcall_debug=1?

Re: [PATCH] tracing/fastboot: document the need of initcall_debug

[Ingo Molnar]

* Li Zefan <lizf@cn.fujitsu.com> wrote:

> Ingo Molnar wrote:
> > * Li Zefan <lizf@cn.fujitsu.com> wrote:
> > 
> >> To use boot tracer, one should pass initcall_debug as well as
> >> ftrace=initcall to the command line.
> > 
> > I think both should be auto-enabled if BOOT_TRACER is enabled, for 
> > ease of use - agreed?
> 
> If both are auto-enabled, we'll always do boot tracing. But we 
> want BOOT_TRACER to be enabled and only enable boot tracing when 
> it's needed.
> 
> But maybe we can make ftrace=initcall implies initcall_debug=1?

That's reasonable indeed.

	Ingo

Re: [PATCH] tracing/fastboot: document the need of initcall_debug

[Frederic Weisbecker]

On Mon, Jun 29, 2009 at 11:14:22AM +0200, Ingo Molnar wrote:
> 
> * Li Zefan <lizf@cn.fujitsu.com> wrote:
> 
> > Ingo Molnar wrote:
> > > * Li Zefan <lizf@cn.fujitsu.com> wrote:
> > > 
> > >> To use boot tracer, one should pass initcall_debug as well as
> > >> ftrace=initcall to the command line.
> > > 
> > > I think both should be auto-enabled if BOOT_TRACER is enabled, for 
> > > ease of use - agreed?
> > 
> > If both are auto-enabled, we'll always do boot tracing. But we 
> > want BOOT_TRACER to be enabled and only enable boot tracing when 
> > it's needed.
> > 
> > But maybe we can make ftrace=initcall implies initcall_debug=1?
> 
> That's reasonable indeed.
> 
> 	Ingo

Yeah.

Although I wonder if this tracer is still useful.
It was first written to debug fastboot, to get more
than the initcall_debug output, ie: the scheduling
events but now I guess the latter is not useful
anymore. And using initcall_debug already does the
job of printing the initcall events.

What do you think?

Re: [PATCH] tracing/fastboot: document the need of initcall_debug

[Ingo Molnar]

* Frederic Weisbecker <fweisbec@gmail.com> wrote:

> On Mon, Jun 29, 2009 at 11:14:22AM +0200, Ingo Molnar wrote:
> > 
> > * Li Zefan <lizf@cn.fujitsu.com> wrote:
> > 
> > > Ingo Molnar wrote:
> > > > * Li Zefan <lizf@cn.fujitsu.com> wrote:
> > > > 
> > > >> To use boot tracer, one should pass initcall_debug as well as
> > > >> ftrace=initcall to the command line.
> > > > 
> > > > I think both should be auto-enabled if BOOT_TRACER is enabled, for 
> > > > ease of use - agreed?
> > > 
> > > If both are auto-enabled, we'll always do boot tracing. But we 
> > > want BOOT_TRACER to be enabled and only enable boot tracing when 
> > > it's needed.
> > > 
> > > But maybe we can make ftrace=initcall implies initcall_debug=1?
> > 
> > That's reasonable indeed.
> > 
> > 	Ingo
> 
> Yeah.
> 
> Although I wonder if this tracer is still useful. It was first 
> written to debug fastboot, to get more than the initcall_debug 
> output, ie: the scheduling events but now I guess the latter is 
> not useful anymore. And using initcall_debug already does the job 
> of printing the initcall events.
> 
> What do you think?

Arjan is/was a frequent user of it. I think some neat stuff came out 
of it: the trace can be fed into sysprof/ftrace and can be 
visualized.

If we remove it we should first provide a replacement perfcounters 
feature for it. Something like a special sw counter that 'buffers' 
its events and so can be enabled during early bootup by the kernel, 
and disabled once init is executed. If user-space creates a counter 
on that event then it gets to read all the boot-time events in a 
stream.

Or something like that. That would integrate the boot tracer 
functionality into perfcounters tooling. We could do a 'perf report' 
display of boot delays for example, and other neat stuff. Sounds 
extremely useful and more usable than the boot tracer because this 
special 'boot delays' event would always be there and can be used by 
the regular 'perf' tooling to inspect bootup properties.

	Ingo

[tip:tracing/urgent] tracing/fastboot: Document the need of initcall_debug

[tip-bot for Li Zefan]

Commit-ID:  238a24f626628cb16a3015f332d649f08246ca89
Gitweb:     http://git.kernel.org/tip/238a24f626628cb16a3015f332d649f08246ca89
Author:     Li Zefan <lizf@cn.fujitsu.com>
AuthorDate: Mon, 29 Jun 2009 15:55:10 +0800
Committer:  Ingo Molnar <mingo@elte.hu>
CommitDate: Mon, 29 Jun 2009 10:22:10 +0200

tracing/fastboot: Document the need of initcall_debug

To use boot tracer, one should pass initcall_debug as well as
ftrace=initcall to the command line.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <4A48735E.9050002@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>


---
 kernel/trace/Kconfig |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 1551f47..019f380 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -226,13 +226,13 @@ config BOOT_TRACER
 	  the timings of the initcalls and traces key events and the identity
 	  of tasks that can cause boot delays, such as context-switches.
 
-	  Its aim is to be parsed by the /scripts/bootgraph.pl tool to
+	  Its aim is to be parsed by the scripts/bootgraph.pl tool to
 	  produce pretty graphics about boot inefficiencies, giving a visual
 	  representation of the delays during initcalls - but the raw
 	  /debug/tracing/trace text output is readable too.
 
-	  You must pass in ftrace=initcall to the kernel command line
-	  to enable this on bootup.
+	  You must pass in initcall_debug and ftrace=initcall to the kernel
+	  command line to enable this on bootup.
 
 config TRACE_BRANCH_PROFILING
 	bool