linux-kernel - Re: 2.6.29-rc4 regression

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Message-ID: <499961AF.8030909@klingt.org>
Date:	Mon, 16 Feb 2009 13:53:03 +0100
From:	Tim Blechmann <tim@...ngt.org>
To:	Robert Richter <robert.richter@....com>
CC:	oprofile-list@...ts.sf.net, linux-kernel@...r.kernel.org
Subject: Re: 2.6.29-rc4 regression

>>> still, I can not reproduce this with my tests with v2.6.29-rc4. The
>>> regression on the systems I have runs fine on rc4. On the system you
>>> have, is commit b99170288421c79f0c2efa8b33e26e65f4bb7fb8 the first bad
>>> one? If so, I will split the patch into smaller pieces to find the
>>> change that introduces the bug.
>> i got revision df13b31c286b3e91c556167954eda088d90a4295 working, by not
>> resetting the counter width:
>>
>> diff --git a/arch/x86/oprofile/op_model_ppro.c b/arch/x86/oprofile/op_model_ppro.c
>> index 12e207a..f0e019d 100644
>> --- a/arch/x86/oprofile/op_model_ppro.c
>> +++ b/arch/x86/oprofile/op_model_ppro.c
>> @@ -76,12 +76,14 @@ static void ppro_setup_ctrs(struct op_msrs const * const msrs)
>>  			return;
>>  	}
>>  
>> +#if 0
>>  	if (cpu_has_arch_perfmon) {
>>  		union cpuid10_eax eax;
>>  		eax.full = cpuid_eax(0xa);
>>  		if (counter_width < eax.split.bit_width)
>>  			counter_width = eax.split.bit_width;
>>  	}
>> +#endif
>>
>>
>> this tweak did not work on later kernels, that i tested, though, and i 
>> haven't had time to look into it in more detail.

hm, i just tried to compile 2.6.28 with this patch applied, and there
the NMIs are delivered correctly.

> Thanks Tim, on later kernels, is it the behaviour you mentioned that
> no NMIs are delivered and you do not receive any NMI?

on the current 2.6.29-rc5, no NMIs are delivered. however i have also
applied the performance counter branch from tip, maybe that interferes
with oprofile?
will try to compile a clean linus/master with this patch later ...

tim

-- 
tim@...ngt.org
http://tim.klingt.org

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