From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner+w=401wt.eu-S1752558AbYJ0Pn3@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1752558AbYJ0Pn3 (ORCPT <rfc822;w@1wt.eu>);
	Mon, 27 Oct 2008 11:43:29 -0400
Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751210AbYJ0PnS
	(ORCPT <rfc822;linux-kernel-outgoing>);
	Mon, 27 Oct 2008 11:43:18 -0400
Received: from mx3.mail.elte.hu ([157.181.1.138]:42555 "EHLO mx3.mail.elte.hu"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1750866AbYJ0PnR (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Mon, 27 Oct 2008 11:43:17 -0400
Date: Mon, 27 Oct 2008 16:43:01 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>,
       Linux Kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] [RESEND v2] tracing/ftrace: Introduce the big kernel
	lock tracer
Message-ID: <20081027154301.GM5704@elte.hu>
References: <48FF928F.1010300@gmail.com> <48FF93D1.4090008@gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <48FF93D1.4090008@gmail.com>
User-Agent: Mutt/1.5.18 (2008-05-17)
X-ELTE-VirusStatus: clean
X-ELTE-SpamScore: -1.5
X-ELTE-SpamLevel: 
X-ELTE-SpamCheck: no
X-ELTE-SpamVersion: ELTE 2.0 
X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00,DNS_FROM_SECURITYSAGE autolearn=no SpamAssassin version=3.2.3
	-1.5 BAYES_00               BODY: Bayesian spam probability is 0 to 1%
	[score: 0.0000]
	0.0 DNS_FROM_SECURITYSAGE  RBL: Envelope sender in
	blackholes.securitysage.com
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


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

> diff --git a/lib/kernel_lock.c b/lib/kernel_lock.c
> index 01a3c22..45828b2 100644
> --- a/lib/kernel_lock.c
> +++ b/lib/kernel_lock.c
> @@ -9,6 +9,7 @@
>  #include <linux/module.h>
>  #include <linux/kallsyms.h>
>  #include <linux/semaphore.h>
> +#include <trace/bkl.h>
>  
>  /*
>   * The 'big kernel lock'
> @@ -107,6 +108,37 @@ static inline void __unlock_kernel(void)
>  	preempt_enable();
>  }
>  
> +#ifdef CONFIG_BKL_TRACER
> +static void lock_kernel_trace(void)
> +{
> +	int cpu;
> +	struct bkl_trace_acquire trace;
> +
> +	preempt_disable();
> +	cpu = raw_smp_processor_id();
> +	preempt_enable();
> +
> +	trace.acquire_req_time = cpu_clock(cpu);
> +	__lock_kernel();
> +	trace.acquire_time = cpu_clock(cpu);
> +	trace_bkl_acquire(&trace);
> +}
> +
> +static void unlock_kernel_trace(void)
> +{
> +	struct bkl_trace_release trace;
> +	trace.release_time = cpu_clock(raw_smp_processor_id());
> +	trace_bkl_release(&trace);
> +	__unlock_kernel();
> +}
> +
> +#else
> +
> +#define lock_kernel_trace() __lock_kernel()
> +#define unlock_kernel_trace() __unlock_kernel()
> +
> +#endif

hm, this looks a bit ugly.

are you aware of the tip/kill-the-BKL branch? It's an old-ish but 
otherwise sane branch that needs some refreshing (hence it's not part 
of tip/master).

Once we have that "kill the BKL by turning it into a mutex" feature 
alive, and have fixed the places that rely on odd properties of the 
BKL, the BKL becomes just an ordinary mutex and we could trace its 
latencies via the existing lockdep/lockstat callbacks.

and we could trace all the other mutexes as well.

	Ingo