Timekeeping problem: can't read pseudoperformance counters with rdpmc

Hi,

I have recently become concerned about obtaining accurate (non-drifting) and precise (fine-grained) timestamps within a Windows guest VM running on ESXi 4.0. I felt like I need to read real time from host machine instead of apparent time, and it seems that accessing Pseudoperformance Counters described in the official Timekeeping in VMware VMs whitepaper should do the trick. I followed the instructions provided in the whitepaper, but I can’t get the rdpmc instruction to work.

I added the line “monitor_control.pseudo_perfctr = TRUE” to the .vmx config file, and then tried to assemble the following code using masm32, but I keep on getting the error “rdpmc-test.asm(35) : error A2085: instruction or register not accepted in current CPU mode” (this is the line with rdpmc invocation). I am using VMware ESXi 4.0, and the same problem occurs on Windows XP 32-bit as well as Windows 7 32-bit guest machines. What am I doing wrong?

(rdpmc-test.asm)

    include \masm32\include\masm32rt.inc

    .data?

      value dd ?

 

    .data

      item dd 0

 

    .code

start:

    call main

    inkey

    exit

main proc

 

    print "rdpmc-test",13,10

    pusha

    mov ecx,10001H

    rdpmc    

    ;print str$(eax),13,10

   popa

    ret

main endp

 

end start

(makeit.bat)

@echo off

 

    if exist "rdpmc-test.obj" del "rdpmc-test.obj"
    if exist "rdpmc-test.exe" del "rdpmc-test.exe"

 

    \masm32\bin\ml /c /coff "rdpmc-test.asm"
    if errorlevel 1 goto errasm

 

    \masm32\bin\PoLink /SUBSYSTEM:CONSOLE "rdpmc-test.obj"
    if errorlevel 1 goto errlink
    dir "rdpmc-test.*"
    goto TheEnd

 

  :errlink
    echo _
    echo Link error
    goto TheEnd

 

  :errasm
    echo _
    echo Assembly Error
    goto TheEnd
   
  :TheEnd

 

pause

(Error output)

Microsoft (R) Macro Assembler Version 6.14.8444
Copyright (C) Microsoft Corp 1981-1997.  All rights reserved.

 

Assembling: rdpmc-test.asm
rdpmc-test.asm(35) : error A2085: instruction or register not accepted in current CPU mode
_
Assembly Error

Press any key to continue . . .

Thanks

Tomasz Szreder