linux-kernel - Re: [PATCH] [RESEND v2] tracing/ftrace: Introduce the big kernel lock tracer

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Date:	Mon, 27 Oct 2008 16:43:01 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] [RESEND v2] tracing/ftrace: Introduce the big kernel
	lock tracer


* Frederic Weisbecker <fweisbec@...il.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
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