linux-kernel - Re: irq-disabled vs vmap vs text

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Message-ID: <20090217171845.GA14435@Krystal>
Date:	Tue, 17 Feb 2009 12:18:45 -0500
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Masami Hiramatsu <mhiramat@...hat.com>,
	Nick Piggin <npiggin@...e.de>,
	Peter Zijlstra <peterz@...radead.org>,
	akpm <akpm@...ux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Jim Keniston <jkenisto@...ibm.com>
Subject: Re: irq-disabled vs vmap vs text_poke

* Steven Rostedt (rostedt@...dmis.org) wrote:
> 
> On Tue, 17 Feb 2009, Masami Hiramatsu wrote:
> > 
> > Thanks, I think text_poke() doesn't need high performance currently,
> > because it's not called so frequently, nor from the normal operation.
> > 
> > However, Would dynamic ftrace need performance?
> 
> Are you talking about replacing what dynamic ftrace does now with 
> text_poke? Well, It takes just under a second right now to do all the 
> conversions. Looking at the list on my booted box, it converts 19805 
> locations. It takes care to run stop machine, and it also has code to 
> handle NMIs on the other CPUS while it runs.
> 
> Changing text must be done extremely carefully on a running box. If the 
> code being changed is also executed on another CPU then you will most 
> likely take a GPF on that CPU.
> 
> Also, every arch must do things a bit different, due to the way modules 
> are handled.
> 
> -- Steve
> 

Anyway dynamic ftrace only need to do code patching at early boot,
right? Or do you need also to patch the call sites a bit later too ?
Because there is a text_poke_early for that purpose : modifying code
when it is still writable.

Mathieu


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