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Bug 141234 - gentoo-sources-2.6.16-r13 cpufreq reports wrong frequency on Pentium 4.
Summary: gentoo-sources-2.6.16-r13 cpufreq reports wrong frequency on Pentium 4.
Status: RESOLVED UPSTREAM
Alias: None
Product: Gentoo Linux
Classification: Unclassified
Component: [OLD] Core system (show other bugs)
Hardware: x86 Linux
: Normal normal
Assignee: Gentoo Kernel Bug Wranglers and Kernel Maintainers
URL: http://bugzilla.kernel.org/show_bug.c...
Whiteboard:
Keywords:
Depends on:
Blocks:
 
Reported: 2006-07-20 21:30 UTC by Timothy Stotts
Modified: 2007-04-29 14:20 UTC (History)
0 users

See Also:
Package list:
Runtime testing required: ---

Attachments
Values of all cpufreq entires under /sys/devices/system/cpu/cpu0/cpufreq/ (p4_cpufreq_sys_values.txt,927 bytes, text/plain)
2006-07-20 21:32 UTC, Timothy Stotts 		Details
/proc/cpuinfo when driver is NOT loaded (p4_cpuinfo__p4-clockmod_not_loaded.txt,419 bytes, text/plain)
2006-07-20 21:32 UTC, Timothy Stotts 		Details
/proc/cpuinfo when driver is IS loaded (p4_cpuinfo__p4-clockmod_is_loaded.txt,419 bytes, text/plain)
2006-07-20 21:33 UTC, Timothy Stotts 		Details
Kernel configuration, gentoo-sources-2.6.16-r13 (config-2.6.16-gentoo-r13patr1,41.04 KB, text/plain)
2006-07-20 21:34 UTC, Timothy Stotts 		Details
View All Add an attachment (proposed patch, testcase, etc.)

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Description Timothy Stotts 2006-07-20 21:30:03 UTC 
Have a desktop with an old Pentium 4 processor (1300 MHz).
gentoo-sources-2.6.16-r13

Expected:
    /proc/cpuinfo to display a current and valid CPU MHz at all times
Actual:
    While 'p4-clockmod' is loaded, the 'cpu MHz' value in /proc/cpuinfo does not correspond to a real frequency.

How to Reproduce:
    (1) configure a Pentium 4 machine with kernel with cpufreq compiled-in and p4-clockmod as module (bug unaffected by compiled-in/module)
    (2) examine /proc/cpuinfo to notice realistic frequency value
    (3) #modprobe p4-clockmod
    (4) notice that /proc/cpuinfo displays an unrealistic frequency value
    (5) #modprobe -r p4-clockmod
    (6) notice that /proc/cpuinfo displays realistic frequency value again

Timing a perl script that does 10*10^8 integer additions, the top cpufreq frequency setting is in fact the same speed as the normal frequency. All intermediate values do in fact adjust the processor speed. However, the value displayed in /proc/cpuinfo is invalid so long as the cpufreq driver is loaded.
Comment 1 Timothy Stotts 2006-07-20 21:32:03 UTC 
Created attachment 92367 [details]
Values of all cpufreq entires under /sys/devices/system/cpu/cpu0/cpufreq/
Comment 2 Timothy Stotts 2006-07-20 21:32:50 UTC 
Created attachment 92368 [details]
/proc/cpuinfo when driver is NOT loaded
Comment 3 Timothy Stotts 2006-07-20 21:33:22 UTC 
Created attachment 92370 [details]
/proc/cpuinfo when driver is IS loaded
Comment 4 Timothy Stotts 2006-07-20 21:34:09 UTC 
Created attachment 92371 [details]
Kernel configuration, gentoo-sources-2.6.16-r13
Comment 5 Daniel Drake (RETIRED) gentoo-dev 2006-08-12 04:34:44 UTC 
Please confirm that this is reproducible on the latest stable kernel (currently 2.6.17), and if so, check whether or not it is fixed in the latest development kernel (currently 2.6.18-rc4)
Comment 6 Timothy Stotts 2006-08-12 06:38:29 UTC 
I only have one (1) Pentium 4 machine, which is a dedicated server that cannot be rebooted frequently.  I will report back upon updating to 2.6.18 stable (when it is released).
Comment 7 Timothy Stotts 2006-09-22 11:29:49 UTC 
Confirmed that bug is upstream problem. Reproducible with 2.6.18 vanilla.

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