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Tasklist

FS#33747 - Incorrect CPU frequency reported when overclocked and using frequency scaling

Attached to Project: Arch Linux
Opened by Marisa Kirisame (Sayachan) - Thursday, 07 February 2013, 11:00 GMT
Last edited by Tobias Powalowski (tpowa) - Saturday, 09 February 2013, 07:44 GMT
Task Type Bug Report
Category Kernel
Status Closed
Assigned To No-one
Architecture All
Severity Low
Priority Normal
Reported Version
Due in Version Undecided
Due Date Undecided
Percent Complete 100%
Votes 0
Private No

Details

Description:

When overclocking the CPU and also having frequency scaling enabled (Intel SpeedStep on the BIOS in this case), the kernel still shows the stock speeds. It seems this is only a visual problem, since the calculated BogoMIPS, for example, is correct. If I disable frequency scaling, this problem does not happen.

This has been happening for quite a long while, can't really remember since what kernel version.

Additional info:

Here are the contents of /proc/cpuinfo
- Frequency scaling enabled: http://sprunge.us/OeNZ
- Frequency scaling disabled: http://sprunge.us/PJYJ

The stock speed of my Q8400 is 2.66GHz, I have the FSB changed from 333 to 395MHz, so the actual speed should be 3.16GHz.

It seems this has been also reported in other places, although not resolved: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/379873

Steps to reproduce:

Changing the FSB clock speed and enabling frequency scaling on the BIOS, while on Linux, at any load the frequency reported by the kernel should be incorrect.
This task depends upon

Closed by  Tobias Powalowski (tpowa)
Saturday, 09 February 2013, 07:44 GMT
Reason for closing:  Not a bug
Comment by Jan de Groot (JGC) - Thursday, 07 February 2013, 14:32 GMT
This is not a bug in the kernel, but the way things are designed. Linux reports speeds as retrieved from the ACPI tables. Your system BIOS decides what gets stored there, so if your BIOS decides to fill these tables with default values, you'll get the default values. This also means that even if the BIOS would initialize them correctly, any software that performs overclocking after the system has booted results in wrong frequencies.

When you load cpufreq, /proc/cpuinfo shows whatever is retrieved from the cpufreq subsystem, so that explains why that value is wrong too.
Comment by Marisa Kirisame (Sayachan) - Thursday, 07 February 2013, 14:34 GMT
I see... So is there any way to correct it? I see Windows has no issues whatsoever.

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