linux-kernel - Re: [PATCH 2/6] Unified trace buffer

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Message-ID: <alpine.DEB.1.10.0809300805140.30533@gandalf.stny.rr.com>
Date:	Tue, 30 Sep 2008 08:06:50 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Ingo Molnar <mingo@...e.hu>
cc:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Mathieu Desnoyers <compudj@...stal.dyndns.org>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [PATCH 2/6] Unified trace buffer


On Tue, 30 Sep 2008, Ingo Molnar wrote:

> 
> * Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> > +void ring_buffer_lock(struct ring_buffer *buffer, unsigned long *flags)
> > +{
> > +	struct ring_buffer_per_cpu *cpu_buffer;
> > +	int cpu;
> > +
> > +	local_irq_save(*flags);
> > +
> > +	for_each_buffer_cpu(buffer, cpu) {
> > +		cpu_buffer = buffer->buffers[cpu];
> > +		spin_lock(&cpu_buffer->lock);
> > +	}
> > +}
> 
> hm, that's rather unintelligent and needs to be fixed.

hm, why?  It is ordered locking based on the cpu value. This is exactly 
what ftrace did as well.  The unlock even goes backwards max_cpu to 0.

But version 2 of this code will drop both ring_buffer_lock and unlock, but 
that will come later.

-- Steve

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