p4-clockmod reports frequencies faster than CPU

p4-clockmod reports frequencies faster than CPU

[Daniel Drake]

Hi,

A Gentoo user at http://bugs.gentoo.org/141234 reports that the 
p4-clockmod cpufreq driver reports bad frequencies for his 1300mhz 
Pentium 4 processor:

# cat sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies
525000 787500 1050000 1312500 1575000 1837500 2100000

The last 3 are obviously wrong.

Unfortunately as this is a production system it's not easy to test other 
kernels, so this has only been reproduced on a Gentoo-patched 2.6.16. 
However the Gentoo patches don't modify cpufreq at all and are generally 
quite minimal.


/proc/cpuinfo output is here:
http://bugs.gentoo.org/attachment.cgi?id=92370&action=view

Does any more info need to be provided?

Thanks,
Daniel

RE: p4-clockmod reports frequencies faster than CPU

[Pallipadi, Venkatesh]

 

>-----Original Message-----
>From: cpufreq-bounces@lists.linux.org.uk 
>[mailto:cpufreq-bounces@lists.linux.org.uk] On Behalf Of Daniel Drake
>Sent: Monday, August 21, 2006 9:11 AM
>To: cpufreq@lists.linux.org.uk
>Cc: zwane@commfireservices.com
>Subject: p4-clockmod reports frequencies faster than CPU
>
>Hi,
>
>A Gentoo user at http://bugs.gentoo.org/141234 reports that the 
>p4-clockmod cpufreq driver reports bad frequencies for his 1300mhz 
>Pentium 4 processor:
>
># cat sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies
>525000 787500 1050000 1312500 1575000 1837500 2100000
>
>The last 3 are obviously wrong.
>
>Unfortunately as this is a production system it's not easy to 
>test other 
>kernels, so this has only been reproduced on a Gentoo-patched 2.6.16. 
>However the Gentoo patches don't modify cpufreq at all and are 
>generally 
>quite minimal.
>
>
>/proc/cpuinfo output is here:
>http://bugs.gentoo.org/attachment.cgi?id=92370&action=view
>
>Does any more info need to be provided?

The root of the problem seems to be this line at
arch/i386/kernel/cpu/cpufreq/speedstep-lib.c:pentium4_get_frequency()

if (c->x86_model < 2)
	mult = msr_lo >> 27;

The CPU model on this system here is 0. As I see in the documentation,
multiplier is not defined in MSR_EBC_FREQUENCY_ID for model 0. So, we
are getting the wrong estimate of the processor frequency.

Dominik may have more history about this.
Dominik: did this >> 27 work on any P4 with model 0 and 1 at all?

Note that this is only a reporting issue. Even with this bug, top speed
of the CPU will always be 1.3 and with P4_clock mod, CPU speed will vary
according to scale by (1/8th) for every lower P-state.

Thanks,
Venki

Thanks,
Venki

Re: p4-clockmod reports frequencies faster than CPU

[Dominik Brodowski]

See bug #7186 now at

http://bugzilla.kernel.org/show_bug.cgi?id=7186

Thanks,
	Dominik