linux-kernel - Re: [PATCH 0/3] ring-buffer: less locking and only disable preemption

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Date:	Mon, 6 Oct 2008 13:13:48 -0400
From:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <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>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [PATCH 0/3] ring-buffer: less locking and only disable
	preemption

* Steven Rostedt (rostedt@...dmis.org) wrote:
> 
> On Sat, 4 Oct 2008, Mathieu Desnoyers wrote:
> > 
> > Or use this code, based on a temporary breakpoint, to do the code
> > patching (part of the -lttng tree). It does not require stop_machine at
> > all and is nmi safe.
> > 
> 
> When this is supported for all archs, and can be done at all functions 
> then I could use it.
> 

How about incrementally using this piece of infrastructure when
available on a given architecture ? This way we keep a sub-optimal
fall-back for archs which does not support NMI-safe code patching and
incrementally get the optimal behavior. Otherwise, we would require any
new architecture to implement that up-front, which I doubt is a good
idea.

> I may just have the arch specific code use it, but we'll see.
> 
> Also, how good is it at patching 20,000 call sites?
> 

Can be done really fast using a hash table, see my previous mail.

Mathieu

> -- Steve
> 

-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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