linux-kernel - Re: perf sched record hangs machine

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Date:	Wed, 23 Sep 2009 10:52:48 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	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

On Wed, 2009-09-23 at 12:48 +0400, Cyrill Gorcunov wrote:
> On 9/23/09, Cyrill Gorcunov <gorcunov@...il.com> wrote:
> > On 9/23/09, Ingo Molnar <mingo@...e.hu> wrote:
> >>
> >> * 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'.
> >>
> >
> > May it wait till evening (i'll back from office and take a look)?
> >
> >> This is a lot cleaner and a lot less error-prone than the direct
> >> frobbing of the function pointers.
> >>
> >> 	Ingo
> >>
> >
> 
> Btw, meanwhile Chris may try to pass lapic boot-option in attempt to
> reenable apic via msr registers. Also (iirc) i feel we may be hiding
> errors if complete noop apic would be used since i belive we need to
> check out under which condition a particular operation is called and
> when apic is disabled it's mean we're switched to UP mode and
> inter-cpu interrupts are under suspicion too. Will take a look during
> ~6 hours ;)

Thing is, this is a self-ipi, nothing inter-cpu about it.
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