Hi everybody!
System: AOpen i915GMm-HFS motherboard, kernel 2.6.16
CPU: Intel(R) Pentium(R) M processor 1.86GHz stepping 08
During startup a BogoMips value of 3730.21 is calculated. That
should be the correct value for the cpu running at full speed. But:
"cat /proc/cpuinfo" on the idle system displays the correct cpu speed, but
a wrong bogomips value:
cpu MHz : 800.000
bogomips : 3730.21
"cat /proc/cpuinfo" on the busy system displays the correct cpu speed
too, but
again a wrong bogomips value:
cpu MHz : 1867.000
bogomips : 8705.38
The relevant snippets from .config:
CONFIG_X86_PC=y
CONFIG_MPENTIUMM=y
CONFIG_CPU_FREQ=y
CONFIG_CPU_FREQ_TABLE=y
CONFIG_CPU_FREQ_DEBUG=y
CONFIG_CPU_FREQ_STAT=y
CONFIG_CPU_FREQ_STAT_DETAILS=y
CONFIG_CPU_FREQ_DEFAULT_GOV_PERFORMANCE=y
CONFIG_CPU_FREQ_GOV_PERFORMANCE=y
CONFIG_CPU_FREQ_GOV_POWERSAVE=y
CONFIG_CPU_FREQ_GOV_USERSPACE=y
CONFIG_CPU_FREQ_GOV_ONDEMAND=y
CONFIG_CPU_FREQ_GOV_CONSERVATIVE=y
CONFIG_X86_ACPI_CPUFREQ=y
CONFIG_X86_SPEEDSTEP_CENTRINO=y
CONFIG_X86_SPEEDSTEP_CENTRINO_ACPI=y
cu,
knut
On Tue, 21 Mar 2006, Knut Petersen wrote:
>
> System: AOpen i915GMm-HFS motherboard, kernel 2.6.16
> CPU: Intel(R) Pentium(R) M processor 1.86GHz stepping 08
>
> During startup a BogoMips value of 3730.21 is calculated. That
> should be the correct value for the cpu running at full speed.
That sounds correct. On x86, BogoMips these days is just a measure of how
fast the timestamp counter goes (multiplied by two for totally bogus
reasons), and a Pentium-M should have a fixed-frequency TSC that ticks at
the highest possible frequency of the CPU, regardless of what the real
frequency is.
So your BogoMips of 3730 sounds correct.
> But:
>
> "cat /proc/cpuinfo" on the idle system displays the correct cpu speed, but
> a wrong bogomips value:
>
> cpu MHz : 800.000
> bogomips : 3730.21
No, this is the _right_ bogomips value. Since the TSC is fixed-frequency,
bogomips doesn't change with CPU frequency.
> "cat /proc/cpuinfo" on the busy system displays the correct cpu speed too, but
> again a wrong bogomips value:
>
> cpu MHz : 1867.000
> bogomips : 8705.38
Yeah, looks like cpufreq has (totally incorrectly) scaled up the bogomips
value.
The scaling up should actually happen if the TSC runs at core speed _or_
if bogomips is calculated using the old "decl + jne" loop. So I guess
somebody "fixed" a bug that was a bug on such systems, and broke systems
with a proper fixed-frequency TSC.
DaveJ, does this ring any bells?
Linus
Linus Torvalds schrieb:
>That sounds correct. On x86, BogoMips these days is just a measure of how
>fast the timestamp counter goes (multiplied by two for totally bogus
>reasons), and a Pentium-M should have a fixed-frequency TSC that ticks at
>the highest possible frequency of the CPU, regardless of what the real
>frequency is.
>
>
>
Pentium 4 and Xeon model 3 and above increment the time stamp counter
at a constant rate independent of the current cpu frequency.
All Pentium M, Xeon up to model 2 and the P6 family increment with every
internal processor cycle.
This behaviour is documented in chapter 18.8 of IA-32 Intel? Architecture
Software Developer?s Manual, Volume 3B: System Programming Guide,
Part 2, Order Number: 253669-018, January 2006.
Because of your false assumption of a fixed-frequency TSC, your
conclusions are false too. Scaling of the bogomips values should
really happen, but the start value is wrong. For 800 MHz there
should be a bogomips value of about 1598, for 1867 MHz a value
of about 3730.
You asked for a full /proc/cpuinfo, here it is ...
processor : 0
vendor_id : GenuineIntel
cpu family : 6
model : 13
model name : Intel(R) Pentium(R) M processor 1.86GHz
stepping : 8
cpu MHz : 800.000
cache size : 2048 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 tsc msr pae mce cx8 apic sep mtrr pge mca cmov
pat clflush dts acpi mmx fxsr sse sse2 ss tmpbe nx est tm2
bogomips : 3730.27
cu,
Knut
On Wed, 22 Mar 2006, Knut Petersen wrote:
>
> All Pentium M, Xeon up to model 2 and the P6 family increment with every
> internal processor cycle.
Just to humor me. Try the bogomips loop in user space with something like
the appended (make sure the frequency is fixed to the lowest frequency).
Linus
---
#include <stdio.h>
#include <sys/time.h>
#define read_tsc(r) asm volatile("rdtsc":"=A" (r))
int main(int argc, char **argv)
{
struct timeval a;
unsigned long start, end;
unsigned long mhz, low;
gettimeofday(&a, NULL);
read_tsc(start);
for (;;) {
unsigned long usec;
struct timeval b;
gettimeofday(&b, NULL);
usec = (b.tv_sec - a.tv_sec)*1000000;
usec += b.tv_usec - a.tv_usec;
if (usec >= 1000000)
break;
}
read_tsc(end);
end -= start;
mhz = end / 1000000;
low = end % 1000000;
printf("TSC: %lu.%06lu MHz\n", mhz, low);
return 0;
}
Linus Torvalds wrote:
>On Wed, 22 Mar 2006, Knut Petersen wrote:
>
>
>>All Pentium M, Xeon up to model 2 and the P6 family increment with every
>>internal processor cycle.
>>
>>
>
>Just to humor me. Try the bogomips loop in user space with something like
>the appended (make sure the frequency is fixed to the lowest frequency).
>
> Linus
>
>
No problem ...
linux:~ # cat
/sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies
1867000 1600000 1333000 1067000 800000
linux:~ # echo 800000 >
/sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed;cat
/proc/cpuinfo;./test
processor : 0
vendor_id : GenuineIntel
cpu family : 6
model : 13
model name : Intel(R) Pentium(R) M processor 1.86GHz
stepping : 8
cpu MHz : 800.000
cache size : 2048 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 tsc msr pae mce cx8 apic sep mtrr pge
mca cmov pat clflush dts acpi mmx fxsr sse sse2 ss tmpbe nx est tm2
bogomips : 3730.27
TSC: 798.307872 MHz
linux:~ # echo 1067000 >
/sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed;cat
/proc/cpuinfo;./test
processor : 0
vendor_id : GenuineIntel
cpu family : 6
model : 13
model name : Intel(R) Pentium(R) M processor 1.86GHz
stepping : 8
cpu MHz : 1067.000
cache size : 2048 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 tsc msr pae mce cx8 apic sep mtrr pge
mca cmov pat clflush dts acpi mmx fxsr sse sse2 ss tmpbe nx est tm2
bogomips : 4975.25
TSC: 1064.407897 MHz
linux:~ # echo 1333000 >
/sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed;cat
/proc/cpuinfo;./test
processor : 0
vendor_id : GenuineIntel
cpu family : 6
model : 13
model name : Intel(R) Pentium(R) M processor 1.86GHz
stepping : 8
cpu MHz : 1333.000
cache size : 2048 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 tsc msr pae mce cx8 apic sep mtrr pge
mca cmov pat clflush dts acpi mmx fxsr sse sse2 ss tmpbe nx est tm2
bogomips : 6215.57
TSC: 1330.511688 MHz
linux:~ # echo 1600000 >
/sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed;cat
/proc/cpuinfo;./test
processor : 0
vendor_id : GenuineIntel
cpu family : 6
model : 13
model name : Intel(R) Pentium(R) M processor 1.86GHz
stepping : 8
cpu MHz : 1600.000
cache size : 2048 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 tsc msr pae mce cx8 apic sep mtrr pge
mca cmov pat clflush dts acpi mmx fxsr sse sse2 ss tmpbe nx est tm2
bogomips : 7460.55
TSC: 1596.612533 MHz
linux:~ # echo 1867000 >
/sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed;cat
/proc/cpuinfo;./test
processor : 0
vendor_id : GenuineIntel
cpu family : 6
model : 13
model name : Intel(R) Pentium(R) M processor 1.86GHz
stepping : 8
cpu MHz : 1867.000
cache size : 2048 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 tsc msr pae mce cx8 apic sep mtrr pge
mca cmov pat clflush dts acpi mmx fxsr sse sse2 ss tmpbe nx est tm2
bogomips : 8705.53
TSC: 1862.715048 MHz
I tried kernel _2.6.15_ too - it?s even more broken:
linux:~ # cat /proc/cpuinfo;./test
processor : 0
vendor_id : GenuineIntel
cpu family : 6
model : 13
model name : Intel(R) Pentium(R) M processor 1.86GHz
stepping : 8
cpu MHz : 4347.853
cache size : 2048 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 tsc msr pae mce cx8 apic sep mtrr pge
mca cmov pat clflush dts acpi mmx fxsr sse sse2 ss tmpbe nx est tm2
bogomips : 8702.35
TSC: 1863.086854 MHz
Isn?t that nice? I?m able to overclock my 1.86 MHz cpu to stable 4.35 MHz
with just a passive heatsink ;-)))
cu,
Knut