: allow notsc option for buggy cpus

Hi,

My IBM Thinkpad 600E changes between 100MHz and 400MHz depending if the power is on. This means gettimeofday goes backwards if you boot with the power out (tsc calibrated at 100MHz) and then plug the power in. (tsc is now spinning at 4x speed, so offsets within the HZ timer period are 4x out!).

The answer is to boot with the notsc option, however since the CONFIG_X86_TSC option is enabled for CONFIG_M686, we cannot do this. Saving one indirect function call for do_gettimeofset is not enough of a reason for CONFIG_X86_TSC. Should we trash this option?

Even so, we should really catch these cpus at run time.

Anton

@@ -80,7 +80,6 @@
 fi
 if [ "$CONFIG_M686" = "y" ]; then
    define_int  CONFIG_X86_L1_CACHE_SHIFT 5
-   define_bool CONFIG_X86_TSC y
    define_bool CONFIG_X86_GOOD_APIC y
    define_bool CONFIG_X86_PGE y
    define_bool CONFIG_X86_USE_PPRO_CHECKSUM y

# cat /proc/cpuinfo
processor	: 0
vendor_id	: GenuineIntel
cpu family	: 6
model		: 6
model name	: Mobile Pentium II
stepping	: 10
cache size	: 256 KB
fdiv_bug	: no
hlt_bug		: no
f00f_bug	: no
coma_bug	: no
fpu		: yes
fpu_exception	: yes
cpuid level	: 2
wp		: yes
flags		: fpu vme de pse msr pae mce cx8 sep mtrr pge mca cmov pat pse36 mmx fxsr
bogomips	: 104.44

Intel speedstep CPU.

Intel are being remarkably reluctant on the documentation front. We have the AMD speed change docs, but the intel ones (chipset not cpu based primarily) don't seem to be publically available. In fact the 815M manual looks like someone quite pointedly went through and removed the relevant material before publication

The 600E's CPU doesn't actually use SpeedStep (it's only a 400MHz Mobile Pentium2, SpeedStep made its debut with the 600MHz Mobile Pentium3), but rather some kind of external speed throttling... which accomplishes basically the same thing, and makes one wonder why Intel had to go and trademark the idea of incorporating it into the CPU.

Toshiba laptops and probably others have been doing the same thing for ages now, I once had a Tecra (now sadly deceased) that would throttle from 133MHz to 66MHz (I think) when unplugged.

I think this behaviour can be controlled with tpctl for the Thinkpads and possibly with the Toshiba utils on Toshibas...

David Huggins-Daines              -                     [email protected]
                      http://www.pobox.com/~dhd/

Its external on the 'speedstep' mostly. Take a look at what little docs there are and you can see the mobile PIII chipset does it

If tpctl can do it and we know how it does it then that may be sufficient since the kernel init code can use DMI to find the 600E, tpctl copied code to go to high speed, bogomip it and then drop back.

Alan> If tpctl can do it and we know how it does it then that may be Alan> sufficient since the kernel init code can use DMI to find the Alan> 600E, tpctl copied code to go to high speed, bogomip it and then Alan> drop back.

Well I can confirm that tpctl allows you to disable it and run the cpu at 400MHz all the time, thats what I did for my 600E.

Jes

Isn't that one of the things that the ACPI is for ? Aren't we supposed to use ACPI for this ?

/Matti Aarnio

If you want to trust a large in kernel interpreter of binary only interpreter code from a BIOS vendor be my guest. Im also not sure ACPI will give us the notifications we need, even in the cases where it actually works.

Alan

But is there a reason we don't allow the notsc option at all on certain chipsets? Who would complain if I removed the CONFIG_X86_TSC option from the CONFIG_M686 definition or even got rid of it completely?

Anton

I believe someone had performance reasons. I'm sceptical and I'd tend to agree with your view. Bug Ingo see what he says