Current processor frequency?

BrowserUk has asked for the wisdom of the Perl Monks concerning the following question:

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Re: Current processor frequency? by traveler (Parson) on Aug 01, 2007 at 22:57 UTC
For Win32, SpeedSwitchXP sets it, reports it and has source. Microsoft has a page of information on the topic, but it is mostly GUI oriented. WMI seems the most likely way. Sys::Info::CPU seems to use WMI, and maybe it gets the correct speed or can be tweaked to do so: I know nothing about WMI. `cpuspeed(8)` sets it in linux and may be able to report it. HTH, --traveler	[reply] [d/l]
Re^2: Current processor frequency? by BrowserUk (Patriarch) on Aug 01, 2007 at 23:33 UTC
Excellent information. Many thanks for your help. Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. "Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."	[reply]
Re: Current processor frequency? by FunkyMonk (Chancellor) on Aug 01, 2007 at 21:22 UTC
On Windows XP it's in the registry: Windows Registry Editor Version 5.00 [HKEY_LOCAL_MACHINE\HARDWARE\DESCRIPTION\System\CentralProcessor\0] "Component Information"=hex:00,00,00,00,00,00,00,00,00,00,00,00,01,00, +00,00 "Identifier"="x86 Family 6 Model 15 Stepping 6" "Configuration Data"=hex(9):ff,ff,ff,ff,ff,ff,ff,ff,00,00,00,00,00,00, +00,00 "ProcessorNameString"="Intel(R) Core(TM)2 CPU 6600 @ 2.40GHz +" "VendorIdentifier"="GenuineIntel" "FeatureSet"=dword:a0073fff "~MHz"=dword:0000095a "Update Signature"=hex:00,00,00,00,c6,00,00,00 "Update Status"=dword:00000000 "Previous Update Signature"=hex:00,00,00,00,44,00,00,00 "Platform ID"=dword:00000001 [download] On Debian/GNU (Lenny) Linux it's in /proc/cpuinfo: processor : 0 vendor_id : AuthenticAMD cpu family : 15 model : 47 model name : AMD Athlon(tm) 64 Processor 3000+ stepping : 2 cpu MHz : 1808.830 cache size : 512 KB fpu : yes fpu_exception : yes cpuid level : 1 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge + mca cmov pat pse36 clflush mmx fxsr sse sse2 syscall nx mmxext fxsr_ +opt lm 3dnowext 3dnow up pni lahf_lm bogomips : 3619.93 TLB size : 1024 4K pages clflush size : 64 cache_alignment : 64 address sizes : 40 bits physical, 48 bits virtual power management: ts fid vid ttp tm stc [download] In Windows 98SE it might be in the registry:) `REGEDIT4 [HKEY_LOCAL_MACHINE\Hardware\Description\System\CentralProcessor\0] "VendorIdentifier"="GenuineIntel" "Identifier"="x86 Family 6 Model 8 Stepping 10" "Update Status"=dword:00000002` [download] It's a Celeron 900MHz, IIRC. update: Added 98SE update^2: Corrected 98SE entry	[reply] [d/l] [select]
Re^2: Current processor frequency? by BrowserUk (Patriarch) on Aug 01, 2007 at 21:38 UTC
Sorry, but isn't all of that just the rated maximum clock speed, not the current actual speed? Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. "Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."	[reply]
Re^3: Current processor frequency? by FunkyMonk (Chancellor) on Aug 01, 2007 at 21:40 UTC
Ah, I see. I have no idea, sorry.	[reply] [d/l] [select]
Re^3: Current processor frequency? by Eyck (Priest) on Aug 02, 2007 at 11:10 UTC
Not all of that, /proc/cpuinfo reports both model (which would be your rated maximum clock speed) and current speed (cpu MHz), for example: `model name : Mobile Intel(R) Pentium(R) III CPU - M 1200MHz cpu MHz : 800.00` [download]	[reply] [d/l]
Re: Current processor frequency? by mr_mischief (Monsignor) on Aug 01, 2007 at 22:18 UTC
I'm not an authority on this, but the utilities I've seen that do that sort of reporting usually depend on a device driver that talks to a device on the chipset or through the CPU's Model Specific Registers (MSRs). It seems you'd want to study up on these registers for the chips you want to support, as talking to the chipset opens the door to a lot more things to consider. Update: Since you did mention that pointers on info for other OSes was perhaps helpful in the future, and since it's Open Source and therefore might give some code hints, here's x86info, which at least dumps MSRs for some CPUs.	[reply]
Re: Current processor frequency? by misc (Friar) on Aug 01, 2007 at 22:10 UTC
On linux it's quite simple, the current cpu frequency is stored in the pseudofile /proc/cpuinfo, in the line "^cpu MHz". I have however no idea how one could get the freqeuency the processor is capable...	[reply]
Re^2: Current processor frequency? by Joost (Canon) on Aug 01, 2007 at 22:13 UTC
AFAIK, the rate reported in /proc/cpuinfo is dependent on the specific architecture and kernel version, but usually, it's the cpu frequency at boot time, not the current speed. See http://lwn.net/Articles/162548/ for instance, though I've no idea how reliable that info is. "What should it profit a man, if he should win a flame war, yet lose his cool?"	[reply]
Re^3: Current processor frequency? by misc (Friar) on Aug 02, 2007 at 00:55 UTC
perhaps it's not as easy I thought.. to me it shows the current frequency, although I've got a smp kernel. (2.6.18) Google said the same for most users. e.g. http://docs.huihoo.com/gentoo/resources/document-listing/power-management-guide.html So I'd guess it's dependent on the kernel version, I wasn't able to find something more specific in the kernel documentation. A short research in the kernel sources didn't answer this, too. What google also told me.. There is more info in the files /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_max_freq /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_min_freq cpuinfo_cur_freq is only readable by root on my system, so this could lead again into problems. At least my question how the max frequency can be determined has been answered. :-)	[reply]
Re: Current processor frequency? by Anonymous Monk on Aug 01, 2007 at 22:54 UTC
Why would you want this? It's a completely useless number! On machines with dynamic scaling of the CPU frequency, any number you arrived at would only be valid for the duration of the instruction during which you read it. From the next instruction on, the CPU may have changed speeds.	[reply]
Re^2: Current processor frequency? by BrowserUk (Patriarch) on Aug 01, 2007 at 23:10 UTC
On machines with dynamic scaling of the CPU frequency, any number you arrived at would only be valid for the duration of the instruction during which you read it. With apologies to NationWide: It doesn't work like that! Or rather, I'm not sure that it does. But in anycase, even if it does, the ability to detect that it varies, even if not exactly when it varies, is still useful information. For the why. Go look up the RDTSC instruction and think about how that might be utilised to provide a very high resolution elapsed timer. And then think about how that would be affected if the clock frequency is varying. And finally, how knowing that it does might be used to (at the very least) warn that the VHRT may not be accurate. There is also the possibility that (for example) that there might be an interface to disable the variation; or that changes to the clock rate might be disabled for the duration of (say) a critical section; or ... Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. "Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."	[reply]
Re^2: Current processor frequency? by eric256 (Parson) on Aug 01, 2007 at 23:33 UTC
My linux desktop had it built in, its nice to know if i'm sitting here and my CPU's spike for a long period I can check my processes and see whats happening, i can visual monitor my dual cores and see that they are both be used for something, mine also has temperature info on the CPU's which is probably obtained in a similar way and it helped me figure out the best desk configuration to keep my computer cooled. Is this all useful, i don't know, but i like having it, makes me feel powerful. BTW statistically sampling it will provide data even if each individual sample might not be representative. ;) ___________ Eric Hodges	[reply]


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