linux-kernel - Re: ftrace introduces instability into kernel 2.6.27(-rc2,-rc3)

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Date:	Wed, 20 Aug 2008 11:17:28 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Steven Rostedt <rostedt@...dmis.org>,
	Scott Wood <scottwood@...escale.com>,
	Eran Liberty <liberty@...ricom.com>,
	linux-kernel@...r.kernel.org, linuxppc-dev@...abs.org,
	Steven Rostedt <srostedt@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Nick Piggin <nickpiggin@...oo.com.au>
Subject: Re: ftrace introduces instability into kernel 2.6.27(-rc2,-rc3)

On Tue, 2008-08-19 at 16:58 -0700, Jeremy Fitzhardinge wrote:
> Benjamin Herrenschmidt wrote:
> >> Ok, there are two cases where it's ok :
> >>
> >> 1 - in stop_machine, considering we are not touching code executed in
> >> NMI handlers.
> >> 2 - when using my replace_instruction_safe() which uses a temporary
> >> breakpoint when doing the instruction replacement.
> >>
> >> In those cases you could use text_poke_early().
> >>     
> >
> > Note that vmap/vunmap will be very slow.
> >   
> 
> Don't we have Nick's speedups now?

Not sure what speedups this is, but it's stlil not something you want to
do a lot ... setting up and tearing down MMU mappings isn't something
I'd like to see happening on a per-mcount basis.

Ben

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