huge difference between reported proc speed and /proc/cpuinfo

[Giles]

I recently bought a second hand Compaq Armada E500, advertised as having an 800MHz processor. However, having run DSL on it*, /proc/cpuinfo reports that it's actually running at 647MHz. Now in the past I've noticed very slight differences between reported speed and the speed given by the file, but never anything like this large a difference.

Can anyone think of a good reason why this discrepancy might have emerged? Or have I been deceived as to the specs of this box?

Thanks for looking at this
Toodle-oo
Giles

*I havent had time to install anything yet

[DThor]

That is a little odd, yes. However, interrupt bootup next time and go to the bios page - there'll be something in there that displays the cpu specs.

DT

[Giles]

The BIOS does report a speed of 800MHz, too. I gues it's probably /proc/cpuinfo that's wrong. Would anyone agree?

Toodle-oo
Giles

[antidrugue]

Are you using some kind of cpu frequency management?

Does /sys/devices/system/cpu/cpu0/cpufreq/ contains something? And what about :

lsmod | grep cpu

And

dmesg | grep -i cpu

Or do you have some cpu power management set in the BIOS?

I don't believe /proc/cpuinfo to be wrong, it just reports your actual CPU speed at this precise moment.

[spoon!]

Is this one of those motherboards or BIOSs that lets you set the CPU's speed? Because then you have to make sure the FSB speed and multiplier are set correctly. For example, there are two Pentium III's at 800MHz: the 800 (100x8) and the 800EB (133x6). Can you look at the CPU physically and see what stuff are written on it?

* It's also possible that the person who sold it to you put in a faster CPU than the motherboard supports, so it doesn't run at full speed.
* Does the messages that show up at boot mention what speed it's running at?
* What does "dmidecode -t processor" show under "current speed"?

[Giles]

Thanks for the replies, and apologies for the delay in replying - I'd planned to reply this morning, and had a lovely long answer written out, when my connection to the forums timed out, so I lost it :- (

I've been using 3 different live CDs to test things (DSL 2.3, Slax 5.0.6, and Knoppix 4.0.2), and there've often been different results to a particular test, depending on the distro used. I've tried to pick the most useful output where this was the case

Are you using some kind of cpu frequency management?

Not as far as I know - I hadn't heard of it before A quick google suggests that it's done within the OS, from which I guess that it couldn't have been set up by the previous user and still be having an effect (since the hard drive was wiped...). Can anyone confirm or deny my assumption?

Does /sys/devices/system/cpu/cpu0/cpufreq/ contains something?

No, I'm afraid not - under DSL there's nothing in /sys at all, while under Slax and Knoppix there is stuff in /sys, but nothing in /sys/devices/system/cpu/cpu0.

And what about :

lsmod | grep cpu

there's no output from that on any of the distros.

And

dmesg | grep -i cpu

This gives output in slax and knoppix, slax being slightly more detailed:

Initializing CPU#0
CPU: After generic identify, caps: 0383f9ff 00000000 00000000 00000000 00000000 00000000 00000000
CPU: After vendor identify, caps: 0383f9ff 00000000 00000000 00000000 00000000 00000000 00000000
CPU: L1 I cache: 16K, L1 D cache: 16K
CPU: L2 cache: 256K
CPU: After all inits, caps: 0383f9ff 00000000 00000000 00000040 00000000 00000000 00000000
Intel machine check reporting enabled CPU#0.
CPU0: Intel Pentium III (Coppermine) stepping 06
Brought up 1 CPUs
CPU0 attaching sched-domain:

Or do you have some cpu power management set in the BIOS?

Is this one of those motherboards or BIOSs that lets you set the CPU's speed?

(I think these two points are asking more or less the same question). Unfortunately the closest I can get to a BIOS, by pressing [F10] at boot, is very minimal indeed (to such an extent that I almost feel there must be an alternative somewhere). There was one potentially useful option, to enable or disable "processor numbering", so I tried disabling it, but there was no change.

Can you look at the CPU physically and see what stuff are written on it?

I'm not too great at hardware, but assuming the processor is the thing underneath the massive heat sink and the fan, it say:
L051A365 SL4AK
KC 800/256

INTEL (R)(C) 00

It's also possible that the person who sold it to you put in a faster CPU than the motherboard supports, so it doesn't run at full speed.

I don't think that's the case, as google suggests that the E500 could come with an 800MHz processor when it was new.

Does the messages that show up at boot mention what speed it's running at?

Unfortunately there's a Compaq splash screen, rather than any useful information, and because of the minimal BIOS I can't find out how to get rid of it. Once Linux has started booting both Knoppix and DSL report the proc speed as 647MHz, with the Slax messages simply going too fast for me to work out what it says about the processor (if anything).

* What does "dmidecode -t processor" show under "current speed"?

The dmidecode command isn't recognised in DSL or Slax. knoppix does have it, but doesn't accept the -t flag. However, the output of simply running dmidecode includes a section that seems relevant:

Handle 0x0004
        DMI type 4, 35 bytes.
        Processor Information
                Socket Designation: J1
                Type: Central Processor
                Family: Pentium III
                Manufacturer: Intel
                ID: 86 06 00 00 FF F9 83 03
                Signature: Type 0, Family 6, Model 8, Stepping 6
                Flags:
                     /*I've removed the flags here, as they took up loads of lines
                     /* And I don't think they'll be relevant. If I'm wrong I can put them up, tho
                Version: Intel Pentium III
                Voltage: 1.8V
                External Clock: 100MHz
                Maximum Speed: 800MHz
                Current Speed: 650MHz
                Status: Populated, Enabled
                Upgrade: Daughter board
                L1 Cache Handle: 0x0009
                L2 Cache Handle: 0x000A
                L3 Cache Handle: Not Provided
                Serial Number: Not Specified
                Asset Tag: Not Specified
                Part Number: Not Specified

My guess is that the most useful part is the bit I've put in bold, saying the maximum and current speed, which seems to make sense.

So the situation seems to be that the processor is indeed an 800Mhz, but that it's not being fully used. Am I right in this interpretation, and if so does anyone know that I could do to get round that?

Thanks again for everyone's help, and apologies if I'm being a bit slow... my brain seems to be disintegrating as a result of exams
Toodle-oo
Giles

[DThor]

I don't think you're being slow, you're covering everything in careful detail.

My gut tells me that either some option hidden in an advanced bios page is set oddly, or somehow someone has combined the hardware together in such a manner that the cpu speed isn't optimized. Obviously, if it's the former, you'll want to try and hunt down that mysterious verbose bios page, and if the latter, there's not a lot to do about it.

Unfortunately sometimes manufacturers "dumb down" the interface to stop you from getting your money's worth. :/

Btw, worth noting from "man dmidecode":

BUGS
More often than not, information contained in the DMI tables is inaccurate, incomplete or simply wrong.



DT

[DThor]

Hmmm, lookee here. Seems like there's a power-saving option called "Speedstep" that might be the culprit. That might be the one you referred to, though. Anyway, some good reading here wrt to Linux and this laptop - might get some clues... They also point out that the function keys to control this stuff operate independant of the OS.

DT

[Giles]

Great link DThor Thanks very much.

Seems to explain everything. The "Speedstep" feature is designed to save battery life, so when you're running from battery it reduces processor speed, and when you've got the power cable plugged in you get the full 800Mhz (and there's various info on the page you linked to on changing that setting).

So that's all it was, really - I should've tried running with the power cable...

Thanks again for everyone's help
Toodle-oo
Giles