Date: Wed, 23 Sep 2009 11:20:24 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Chris Malley <mail@chrismalley.co.uk>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>,
       Peter Zijlstra <peterz@infradead.org>,
       Frederic Weisbecker <fweisbec@gmail.com>, linux-kernel@vger.kernel.org,
       Steven Rostedt <rostedt@goodmis.org>
Subject: Re: perf sched record hangs machine
Message-ID: <20090923092024.GA29323@elte.hu>
References: <7863dc4c0909221409v7893bfd3o4b590d5951a233ba@mail.gmail.com> <20090922212453.GB6062@nowhere> <1253686585.7695.84.camel@twins> <20090923073253.GA18022@elte.hu> <20090923074028.GA3078@elte.hu> <aa79d98a0909230044q3548cf0bjda62e05e0400edd6@mail.gmail.com> <aa79d98a0909230148j47232382oe28c6d88eef181c4@mail.gmail.com> <7863dc4c0909230215u2fed3edciec84f93f24d3ae1@mail.gmail.com>
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* Chris Malley <mail@chrismalley.co.uk> wrote:

> 2009/9/23 Cyrill Gorcunov <gorcunov@gmail.com>:
> >
> > 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 ;)
> >
> 
> Hi Cyrill
> 
> Heh, yes that just occurred to me as well.  With the lapic boot option 
> I can't reproduce the problem, and get a good recording every time. 
> Don't know why the BIOS had disabled it (can't see any specific 
> option).

Would still be important to fix the crash - there are boxes where lapics 
are disabled permanently and cannot be re-enabled. (plus most people 
dont touch their defaults and dont add funky boot options - so crashing 
is not an option)

I have such a test-box:

[    0.000000] Using APIC driver default
[    0.000000] ACPI: PM-Timer IO Port: 0x8008
[    0.000000] SMP: Allowing 1 CPUs, 0 hotplug CPUs
[    0.000000] Local APIC disabled by BIOS -- reenabling.
[    0.000000] Could not enable APIC!
[    0.000000] APIC: disable apic facility

Btw., perf events can work even without a lapic (albeit without NMI 
driven sampling):

[    0.052051] Performance Events:
[    0.055138] no APIC, boot with the "lapic" boot parameter to force-enable it.
[    0.056014] no hardware sampling interrupt available.
[    0.060014] p6 PMU driver.
[    0.062955] ... version:                0
[    0.064014] ... bit width:              32
[    0.068014] ... generic registers:      2
[    0.072015] ... value mask:             00000000ffffffff
[    0.076014] ... max period:             000000007fffffff
[    0.080014] ... fixed-purpose events:   0
[    0.084014] ... event mask:             0000000000000003

That's what it did on your box too:

[    0.013679] Performance Events:
[    0.013705] no APIC, boot with the "lapic" boot parameter to force-enable it.
[    0.013783] no hardware sampling interrupt available.
[    0.013826] p6 PMU driver.
[    0.013882] ... version:                0
[    0.013922] ... bit width:              32
[    0.013962] ... generic registers:      2
[    0.014002] ... value mask:             00000000ffffffff
[    0.014045] ... max period:             000000007fffffff
[    0.014088] ... fixed-purpose events:   0
[    0.014128] ... event mask:             0000000000000003

Unfortunately i cannot reproduce the crash you've been seeing. (but i'm 
quite sure it's due to self-IPI not working fine with dummy lapic.)

	Ingo
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