Aproximating the CPU clock rate

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revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20430
Location: In your JS exploiting you and your system

revolution 15 Feb 2015, 14:03

Here is a small utility for approximating the current CPU clock rate.

It is only accurate to about 2 significant digits so don't expect a perfect value. But for a quick check of how your CPU is clocking it is probably good enough.

Code:

include 'win32ax.inc'

.code

proc begin uses edi esi
        locals
                Hz      rd 2
                MHz     rd 1
                speed   rb 1024
        endl
        invoke  GetCurrentProcess
        invoke  SetProcessAffinityMask,eax,1
        rdtsc
        mov     esi,eax
        mov     edi,edx
        invoke  Sleep,500
        rdtsc
        sub     eax,esi
        sbb     edx,edi
        add     eax,eax
        adc     edx,edx
        mov     [Hz+0],eax
        mov     [Hz+4],edx
        mov     ecx,1000000
        div     ecx
        mov     [MHz],eax
        invoke  wsprintf,addr speed,<'Approximate Speed: %I64u Hz (%u MHz)'>,[Hz+0],[Hz+4],[MHz]
        invoke  MessageBox,0,addr speed,'Your current speed',MB_OK
        invoke  ExitProcess,0
endp

.end begin

15 Feb 2015, 14:03

l_inc

Joined: 23 Oct 2009
Posts: 881

l_inc 15 Feb 2015, 14:34

revolution
On modern CPUs the TSC is unrelated to the current CPU clock rate, and in most cases is incremented according to the CPU base frequency.

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15 Feb 2015, 14:34

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20430
Location: In your JS exploiting you and your system

revolution 15 Feb 2015, 16:15

Suggestion on how to fix it for these "modern" CPUs?

15 Feb 2015, 16:15

l_inc

Joined: 23 Oct 2009
Posts: 881

l_inc 15 Feb 2015, 17:03

revolution
Sure. You should read the performance monitor counter values such as the "unhalted core cycles" counter. Sure you need a driver at least for configuring the counters properly.

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15 Feb 2015, 17:03

HaHaAnonymous

Joined: 02 Dec 2012
Posts: 1178
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HaHaAnonymous 15 Feb 2015, 17:19

[ Post removed by author. ]

Last edited by HaHaAnonymous on 28 Feb 2015, 17:56; edited 1 time in total

15 Feb 2015, 17:19

l_inc

Joined: 23 Oct 2009
Posts: 881

l_inc 15 Feb 2015, 17:31

HaHaAnonymous

Quote:

Please define modern...

Pretty much all the Intel CPUs released during the last 10 years (since late P4).

Quote:

The code worked fine for my CPU

It is fine, if you accept any arbitrary value as fine.

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15 Feb 2015, 17:31

HaHaAnonymous

Joined: 02 Dec 2012
Posts: 1178
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HaHaAnonymous 15 Feb 2015, 21:11

[ Post removed by author. ]

Last edited by HaHaAnonymous on 28 Feb 2015, 17:55; edited 1 time in total

15 Feb 2015, 21:11

l_inc

Joined: 23 Oct 2009
Posts: 881

l_inc 15 Feb 2015, 22:53

HaHaAnonymous

Quote:

My CPU box says it runs at 2.6GHz, 2594MHz is precise enough.

As I said before, the TSC "in most cases is incremented according to the CPU base frequency". In your case 2.6GHz is the base frequency. But if you have Turbo Boost enabled, or if you try to change the actual CPU frequency by altering the CPU clock multiplier in the BIOS, you'll still get the 2.6GHz, even though this value wouldn't be correct. Try to compare the value you get from revolution's snippet to the value displayed by the CPU-Z.

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15 Feb 2015, 22:53

HaHaAnonymous

Joined: 02 Dec 2012
Posts: 1178
Location: Unknown

HaHaAnonymous 16 Feb 2015, 00:53

[ Post removed by author. ]

16 Feb 2015, 00:53

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