linux-kernel - Re: [PATCH] tracing: Fix TRACING

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Message-ID: <20090321163328.GH11183@elte.hu>
Date:	Sat, 21 Mar 2009 17:33:28 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Anton Vorontsov <avorontsov@...mvista.com>,
	Steven Rostedt <srostedt@...hat.com>, linuxppc-dev@...abs.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tracing: Fix TRACING_SUPPORT dependency


* Steven Rostedt <rostedt@...dmis.org> wrote:

> 
> On Sat, 21 Mar 2009, Ingo Molnar wrote:
> 
> > 
> > * Anton Vorontsov <avorontsov@...mvista.com> wrote:
> > 
> > > On Fri, Mar 20, 2009 at 08:57:43PM +0100, Ingo Molnar wrote:
> > > > 
> > > > * Anton Vorontsov <avorontsov@...mvista.com> wrote:
> > > > 
> > > > > On Fri, Mar 20, 2009 at 08:04:28PM +0100, Ingo Molnar wrote:
> > > > > > 
> > > > > > * Anton Vorontsov <avorontsov@...mvista.com> wrote:
> > > > > > 
> > > > > > > commit 40ada30f9621fbd831ac2437b9a2a399aad34b00 ("tracing: clean 
> > > > > > > up menu"), despite the "clean up" in its purpose, introduced 
> > > > > > > behavioural change for Kconfig symbols: we no longer able to 
> > > > > > > select tracing support on PPC32 (because IRQFLAGS_SUPPORT isn't 
> > > > > > > yet implemented).
> > > > > > 
> > > > > > Could you please solve this by implementing proper 
> > > > > > irqflag-tracing support? It's been available upstream for almost 
> > > > > > three years. It's needed for lockdep support as well, etc.
> > > > > 
> > > > > Breaking things via clean up patches is an interesting method of 
> > > > > encouraging something to implement. ;-)
> > > > >
> > > > > Surely I'll look into implementing irqflags tracing, but 
> > > > > considering that no one ever needed this for almost three years, 
> > > > > [...]
> > > > 
> > > > Weird, there's no lockdep support?
> > > 
> > > *ashamed*: apparently no such support currently exist for PPC32. ;-)
> > 
> > Hm, do all the tracers even compile on ppc32 with your patch?
> > 
> > We had periodic build failures on weird, unmaintained architectures 
> > that had no irqflags-tracing support and hence didnt know the 
> > raw_irqs_save/restore primitives ...
> > 
> > I'm not trying to make things more difficult for you (and we can 
> > apply your patch if it builds fine and does not cause problems 
> > elsewhere), but there were some real downsides to not having proper 
> > irq APIs ...
> 
> Note, the issue is not with the hooks into local_irq_save/restore, 
> but with the entry.S code. That code is very sensitive where the 
> irqs are enabled and disabled.

i know. What i'm talking about is that non-lockdep architectures 
have the habit of not defining raw_local_irq_save() - which the 
tracing core relies on.

	Ingo
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