linux-kernel - Re: perf sched record hangs machine

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Message-ID: <aa79d98a0909230148j47232382oe28c6d88eef181c4@mail.gmail.com>
Date:	Wed, 23 Sep 2009 12:48:04 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	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 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 ;)
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