From: David Miller <davem@davemloft.net>
To: andi@firstfloor.org
Cc: linux-kernel@vger.kernel.org
Subject: Re: x86's nmi_hz wrt. oprofile's nmi_timer_int.c
Date: Sun, 22 Feb 2009 21:59:06 -0800 (PST) [thread overview]
Message-ID: <20090222.215906.240407314.davem@davemloft.net> (raw)
In-Reply-To: <20090223045159.GR26292@one.firstfloor.org>
From: Andi Kleen <andi@firstfloor.org>
Date: Mon, 23 Feb 2009 05:52:00 +0100
> > Again, the code in nmi_timer_int.c doesn't.
> >
> > It uses the NMI watchdog timer interrupts, it catches DIE_NMI
> > events.
> >
> > > Does that answer your question?
> >
> > Not really.
>
> Ah see what you mean now. The nmi_timer_int code can only
> be active ever when the cpu is not known to nmi_int.c and
> when the nmi watchdog is in io apic mode. But IO apic mode
> doesn't use the fast check/slowdown because it always runs
> at HZ frequency. That only happens in LAPIC mode.
>
> The standard fallback mode for unknown CPU is the non NMI timer
> fallback in oprofile_init, the IO APIC mode happens near never in practice.
Look at the fallback logic, the pure NMI profiler can fail for
a number of reasons, not just because the watchdog is in
I/O APIC mode.
No matter what the failure reason, nmi_int.c is used.
And in some of those cases, the nmi_hz has been decreased to '1'.
next prev parent reply other threads:[~2009-02-23 5:59 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-01-29 23:58 David Miller
2009-01-30 15:01 ` Ingo Molnar
2009-01-30 21:54 ` David Miller
2009-02-02 23:14 ` David Miller
2009-02-03 12:27 ` Ingo Molnar
2009-02-22 17:06 ` Andi Kleen
2009-02-23 4:11 ` David Miller
2009-02-23 4:52 ` Andi Kleen
2009-02-23 5:59 ` David Miller [this message]
2009-02-23 6:34 ` Andi Kleen
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