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

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Date:	Mon, 10 Nov 2008 16:50:00 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	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()

Andi Kleen a écrit :
>>  			oprofile_add_sample(regs, i);
>> +			/*
>> +			 * We need to unmask the apic vector *before*
>> +			 * writing reset_value to msr counter
>> +			 */
>> +			apic_write(APIC_LVTPC, APIC_DM_NMI);
>>  			wrmsrl(msrs->counters[i].addr, -reset_value[i]);
>>  		}
>>  	}
>>  
>> -	/* Only P6 based Pentium M need to re-unmask the apic vector but it
>> -	 * doesn't hurt other P6 variant */
>> -	apic_write(APIC_LVTPC, apic_read(APIC_LVTPC) & ~APIC_LVT_MASKED);
> 
> Did you also test if it really needs to be inside the if () or 
> just before the wrmsrl? 


In my testings, the "if (CTR_OVERFLOWED())" condition is always true.

(I am profiling one event only)

I felt uncomfortable issuing the apic_write() before oprofile_add_sample()

Do you mean doing the apic_write() right at the beginning of the ppro_check_ctrs()
function ?

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