linux-kernel - Re: perf sched record hangs machine

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Date:	Wed, 23 Sep 2009 09:40:28 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Peter Zijlstra <peterz@...radead.org>,
	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Chris Malley <mail@...ismalley.co.uk>,
	linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>
Subject: Re: perf sched record hangs machine


* Ingo Molnar <mingo@...e.hu> wrote:

> 
> * Peter Zijlstra <peterz@...radead.org> wrote:
> 
> >         .size   default_send_IPI_self, .-default_send_IPI_self
> > 
> > Which seems to suggest that cmove is in __prepare_ICR, but I'm not 
> > sure how that can cause a page-fault, as that function is rather 
> > pointer-less.
> > 
> > Did it maybe delay evaluating apic->dest_logical that late, it appear 
> > to be the first usage of that argument?
> > 
> > Ingo, any ideas?
> 
> Yeah, the problem is:
> 
> [    0.042445] Local APIC not detected. Using dummy APIC emulation.
> 
> we shouldnt be trying to program the lapic in that case - all ops 
> should be a NOP, including send-ipi-self. Cyrill?

Cyrill, the right fix would be to define a:

	struct apic apic_none;

with dummy functions injected. Set struct apic *apic to _that_, instead 
of apic_default.

This means that if we manage to detect a local APIC, we will set it to 
apic_default (or some other driver) - but the bootup default will be 'no 
APIC'.

This is a lot cleaner and a lot less error-prone than the direct 
frobbing of the function pointers.

	Ingo
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