linux-kernel - Re: perf sched record hangs machine

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Message-ID: <20090923104100.GA23941@elte.hu>
Date:	Wed, 23 Sep 2009 12:41:00 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	Chris Malley <mail@...ismalley.co.uk>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>
Subject: Re: perf sched record hangs machine


* Cyrill Gorcunov <gorcunov@...il.com> wrote:

> On 9/23/09, Ingo Molnar <mingo@...e.hu> wrote:
> >
> > * Chris Malley <mail@...ismalley.co.uk> wrote:
> >
> >> 2009/9/23 Cyrill Gorcunov <gorcunov@...il.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)
> >
> 
> Ingo, Chris, could you try Peter's patch? It seems like what we need.

It should fix the problem, but also the underlying uncleanliness should 
be fixed as well. We need an apic_none driver template with safe 
methods. Then all the scattered 'is the lapic enabled' open-coded checks 
of global flags can be removed.

	Ingo
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