linux-kernel - Re: [RFC PATCH v4] Unified trace buffer

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Message-ID: <alpine.DEB.1.10.0809260641590.17102@gandalf.stny.rr.com>
Date:	Fri, 26 Sep 2008 06:45:28 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Mathieu Desnoyers <compudj@...stal.dyndns.org>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	prasad@...ux.vnet.ibm.com,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	David Wilder <dwilder@...ibm.com>, hch@....de,
	Martin Bligh <mbligh@...gle.com>,
	Christoph Hellwig <hch@...radead.org>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [RFC PATCH v4] Unified trace buffer


On Fri, 26 Sep 2008, Peter Zijlstra wrote:
> On Thu, 2008-09-25 at 23:20 -0400, Mathieu Desnoyers wrote:
> > 
> > You could also fallback on a 2-level page array when buffer size is >
> > 64MB. The cost is mainly a supplementary pointer dereference, but one
> > more should not make sure a big difference overall.
> 
> I'm still not sure why we don't just link the pages using the page
> frames, we don't need the random access, do we?

Yeah we can go back to that (as ftrace does).

1) It can be very error prone. I will need to encapsulate the logic more.

2) I'm still not sure if crash can handle it.


I was going to reply to Masami with this answer, but it makes things more 
complex.  For v1 (non RFC v1) I wanted to start simple. v2 can have this 
enhancement.

-- Steve

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