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List:       oprofile-list
Subject:    oprofile and NMI
From:       Stephane Eranian <eranian () hpl ! hp ! com>
Date:       2005-12-20 11:46:55
Message-ID: 20051220114655.GE4584 () frankl ! hpl ! hp ! com
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Hello,

I have been looking at the Oprofile source from 2.6.15-rc6
for i386 and I have a question about the NMI setup
has done by nmi_setup() in nmi_int.c.

The call to reserve_lapic_nmi() is made once one some
CPU. That is enough to disable the LAPIC NMI watchdog.
But this is not enough to stop the performance counters
on all CPUS. The NMI watchdog is operating on all CPUS
and is setup in setup_local_APIC(). Yet the
disable_lapic_nmi() will be invoked only on one CPU.
That means that On all but one CPU, the perf counters are
still running and can possibly interrupt while OProfile
is setting itself up.

I have reported this NMI logic problem on lkml
in this message:
	http://marc.theaimsgroup.com/?l=linux-kernel&m=113500459412560&w=3

What is your take on this?

Thanks.

-- 
-Stephane


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