linux-kernel - Re: [PATCH] oprofile: re-arm APIC_DM_NMI in ppro_check

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Date:	Mon, 10 Nov 2008 19:31:35 +0300
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Eric Dumazet <dada1@...mosbay.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Robert Richter <robert.richter@....com>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] oprofile: re-arm APIC_DM_NMI in ppro_check_ctrs()

[Eric Dumazet - Mon, Nov 10, 2008 at 05:19:20PM +0100]
...
>>
>> Hi Eric,
>>
>> for the record
>>
>> 	apic_write(APIC_LVTPC, APIC_DM_NMI);
>>
>> is not just 'unmask' but also *zeroify* (not sure if I wrote this
>> word right :) all fields when the origianl code was just 'unmasking'
>> TPC register
>>
>> 	apic_write(APIC_LVTPC, apic_read(APIC_LVTPC) & ~APIC_LVT_MASKED);
>>
>> that is why apic_read() was in former.
>>
>
> Well, given that APIC_LVTPC is initialized by oprofile init to value APIC_DM_NMI,
> I avoid an apic_read() and just write APIC_DM_NMI again...
>
> Presumably, apic_read(APIC_LVTPC) should return APIC_DM_NMI or APIC_DM_NMI|APIC_LVT_MASKED
>
> Thanks
>

Yes, just grepped the sources -- it seems nobody else touching
this register indeed.
		- Cyrill -
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