linux-kernel - Re: [PATCH 00/12] perf lock: New subcommand "perf lock", for analyzing lock statistics

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Date:	Tue, 26 Jan 2010 16:04:41 +0900
From:	Hitoshi Mitake <mitake@....info.waseda.ac.jp>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Jason Baron <jbaron@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org, Paul Mackerras <paulus@...ba.org>,
	Tom Zanussi <tzanussi@...il.com>,
	Steven Rostedt <srostedt@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Greg Kroah-Hartman <gregkh@...e.de>
Subject: Re: [PATCH 00/12] perf lock: New subcommand "perf lock", for 
	analyzing lock statistics

On Mon, Jan 25, 2010 at 23:48, Peter Zijlstra <peterz@...radead.org> wrote:
> On Mon, 2010-01-25 at 23:15 +0900, Hitoshi Mitake wrote:
>>
>> As Peter told, this patch series depends on lockdep.
>> But, checking dependency and tracing lock events are
>> essentially different things. So I think dividing these is possible.
>
> Still you need quite a lot of instrumentation at the actual lock sites,
> not something you'd want to have on your production machine.
>
>> But, perf depends on debugfs.
>> I don't know about production box well,
>> does your production box turns on debugfs?
>> It seems that debugfs is not a thing for production box...
>
> debugfs isn't a problem to have.

I didn't know that, thanks Peter and Greg!

>
>> And I'm interesting in in-kernel histogram of locks.
>> Is there requirement of it?
>> I have some ideas (not done yet, completely).
>
> No real concrete ideas yet.. One possibility is to add a range,
> bucket_size tuple to perf_event_attr and store the histrogram in the
> mmap() area instead of samples.
>
> One difficulty is how to specify what to make that histogram over.
>
> Anyway, its all open still..
>
>
>

I think my previous patch will helpful for this purpose,
http://lkml.org/lkml/2009/12/13/16
# This patch is too dangerous and too incomplete, please don't use!

I think distributing numerical IDs for lock instances makes things easily.
Distributing IDs means that kernel can know where the lock instances are.
Updating information of ID should be triggered by:

1) booting
   Lock defined by DEFINE_SPINLOCK(), DEFINE_RWLOCK(), etc can be
   corrected into specific section and initialized.
   Like the way of event_trace_init() in kernel/trace/trace_events.c

2) loading/unloading modules
   Lock defined by DEFINE_SPINLOCK(), DEFINE_RWLOCK(), etc can be in .ko files.
   So hooking module loading or unloading will be required.

3) calling spin_lock_init(), rwlock_init(), etc...

It seems that difficulty of drawing histogram came from the running kernel's
lack of knowledge about where the lock instances are, isn't it?

Thanks,
	Hitoshi
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