Passthrough: APIC-Timer too slow (just 2kHz).

Please see the information below. The problem was identified more pecisely after the thread was created.

Old Text:

Hi guys. I recently bought a CNC Milling machine which is controled via parallel port and i am using WinXP 32bit in a VM to get the software going.

My PC does not have on board parallel port so i bought an PCIe extension card.

The Card shows up in the PCI-Devices list as:

06:00.0 Serial controller [0700]: MosChip Semiconductor Technology Ltd. Device [9710:9905]
06:00.2 Parallel controller [0701]: MosChip Semiconductor Technology Ltd. PCIe 9912 Multi-I/O Controller [9710:9912]

So i passed the device through with:

 <hostdev mode='subsystem' type='pci' managed='yes'>
      <driver name='vfio'/>
      <source>
        <address domain='0x0000' bus='0x06' slot='0x00' function='0x0'/>
      </source>
      <alias name='hostdev0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/>
    </hostdev>
    <hostdev mode='subsystem' type='pci' managed='yes'>
      <driver name='vfio'/>
      <source>
        <address domain='0x0000' bus='0x06' slot='0x00' function='0x2'/>
      </source>
      <alias name='hostdev1'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x06' function='0x0'/>
    </hostdev>

At least thats what Unraid creates with my input. I orignially said:

 <hostdev mode='subsystem' type='pci' managed='yes'>
      <driver name='vfio'/>
      <source>
        <address domain='0x0000' bus='0x06' slot='0x00' function='0x0'/>
      </source>
      <alias name='hostdev0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'  multifunction='on'/>
    </hostdev>
    <hostdev mode='subsystem' type='pci' managed='yes'>
      <driver name='vfio'/>
      <source>
        <address domain='0x0000' bus='0x06' slot='0x00' function='0x2'/>
      </source>
      <alias name='hostdev1'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x2'/>
    </hostdev>

But that doesnt get saved. Whatever. It works in Windows XP. Devices detected, drivers installed and the CNC can be controlled.

BUT:  the CNC control program needs a solid connection to the parallel port. It is usually controlling the parallel port with 25kHz update rate, however my windows does reach exactly 2kHz not more, not less.

I tried several expeansion cards and all show the same behavior.  Right now i have a "DS 30020-1" inserted which supports up to 2.5Mbps.

Given its an 8bit serial port, the 2.5Mbps translates to 312.5kHz toggle rate, so its not a hardware limitation.

I kind of hope that anyone can tell be what in unraid / kvm or whatever hold the hardware back...

Additional Info:

i have 2 cores (3, 9) assigned to the VM. Both cores are not in use by other VMs..  (3, 9) is a core/thread-pair. (its a 6C12T cpu)

I played around with the "hpet"-counter and set the present="yes" however this didnt help.

Addionally the VirtIO-Serial driver in WinXP 32bit says "device can not start"

Same with the GT730 thats passed through.

Any ideas would be great.

Whole XML:

<domain type='kvm'>
  <name>Windows XP</name>
  <uuid>216e462b-f93e-f26d-8881-066f3790edb3</uuid>
  <metadata>
    <vmtemplate xmlns="unraid" name="Windows XP" icon="windowsxp.png" os="windowsxp"/>
  </metadata>
  <memory unit='KiB'>1048576</memory>
  <currentMemory unit='KiB'>1048576</currentMemory>
  <memoryBacking>
    <nosharepages/>
    <locked/>
  </memoryBacking>
  <vcpu placement='static'>2</vcpu>
  <cputune>
    <vcpupin vcpu='0' cpuset='3'/>
    <vcpupin vcpu='1' cpuset='9'/>
  </cputune>
  <os>
    <type arch='x86_64' machine='pc-i440fx-2.5'>hvm</type>
  </os>
  <features>
    <acpi/>
    <apic/>
  </features>
  <cpu mode='host-passthrough'>
    <topology sockets='1' cores='1' threads='2'/>
  </cpu>
  <clock offset='localtime'>
    <timer name='rtc' tickpolicy='catchup'/>
    <timer name='pit' tickpolicy='delay'/>
    <timer name='hpet' present='no'/>
  </clock>
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>restart</on_crash>
  <devices>
    <emulator>/usr/local/sbin/qemu</emulator>
    <disk type='file' device='cdrom'>
      <driver name='qemu' type='raw'/>
      <source file='/mnt/user/Shared/pcriver.com_Windows_XP_Pro_SP3_32_bit.iso'/>
      <target dev='hda' bus='ide'/>
      <readonly/>
      <boot order='2'/>
      <address type='drive' controller='0' bus='0' target='0' unit='0'/>
    </disk>
    <disk type='file' device='cdrom'>
      <driver name='qemu' type='raw'/>
      <source file='/mnt/user/Shared/virtio-win-0.1.130.iso'/>
      <target dev='hdb' bus='ide'/>
      <readonly/>
      <address type='drive' controller='0' bus='0' target='0' unit='1'/>
    </disk>
    <disk type='file' device='disk'>
      <driver name='qemu' type='raw' cache='writeback'/>
      <source file='/mnt/user/domains/Windows XP/vdis1k.img'/>
      <target dev='hdc' bus='ide'/>
      <boot order='1'/>
      <address type='drive' controller='0' bus='1' target='0' unit='0'/>
    </disk>
    <controller type='usb' index='0' model='ich9-ehci1'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x7'/>
    </controller>
    <controller type='usb' index='0' model='ich9-uhci1'>
      <master startport='0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0' multifunction='on'/>
    </controller>
    <controller type='usb' index='0' model='ich9-uhci2'>
      <master startport='2'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x1'/>
    </controller>
    <controller type='usb' index='0' model='ich9-uhci3'>
      <master startport='4'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x2'/>
    </controller>
    <controller type='pci' index='0' model='pci-root'/>
    <controller type='ide' index='0'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x1'/>
    </controller>
    <controller type='virtio-serial' index='0'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
    </controller>
    <interface type='bridge'>
      <mac address='52:54:00:ad:6e:a6'/>
      <source bridge='br0'/>
      <model type='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
    </interface>
    <serial type='pty'>
      <target port='0'/>
    </serial>
    <console type='pty'>
      <target type='serial' port='0'/>
    </console>
    <channel type='unix'>
      <source mode='connect'/>
      <target type='virtio' name='org.qemu.guest_agent.0'/>
      <address type='virtio-serial' controller='0' bus='0' port='1'/>
    </channel>
    <input type='tablet' bus='usb'/>
    <input type='mouse' bus='ps2'/>
    <input type='keyboard' bus='ps2'/>
    <graphics type='vnc' port='-1' autoport='yes' websocket='-1' listen='0.0.0.0' keymap='de'>
      <listen type='address' address='0.0.0.0'/>
    </graphics>
    <video>
      <model type='qxl' ram='65536' vram='65536' vgamem='16384' heads='1'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
    </video>
    <hostdev mode='subsystem' type='pci' managed='yes'>
      <driver name='vfio'/>
      <source>
        <address domain='0x0000' bus='0x03' slot='0x00' function='0x0'/>
      </source>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/>
    </hostdev>
    <hostdev mode='subsystem' type='pci' managed='yes'>
      <driver name='vfio'/>
      <source>
        <address domain='0x0000' bus='0x06' slot='0x00' function='0x0'/>
      </source>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x06' function='0x0'/>
    </hostdev>
    <hostdev mode='subsystem' type='pci' managed='yes'>
      <driver name='vfio'/>
      <source>
        <address domain='0x0000' bus='0x06' slot='0x00' function='0x2'/>
      </source>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x08' function='0x0'/>
    </hostdev>
    <memballoon model='virtio'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x09' function='0x0'/>
    </memballoon>
  </devices>
</domain>

Important information to add:

The timing withing the CNC control program is created using the APIC-Timer.

I got the distinct feeling that the emulated or passedthrough? APIC timer has a rather low frequency so the required minium of 25kHz cannot be reached.

Or maybe the interrupt is served not often enough, if emulated. 

I tried to remove the <apic/> from the <features>  to see if the CNC programm has a fallback option or software emulation or whatever.. however it keeps saying that the apic is present. :-(

Any ideas with this addional information?

Meanwhilei confirmed the strange APIC behavior under Windows and Linux  (LinuxCNC based on Debian Wheezy).

See the strange timing in the attached image. 1ms -> 2ms.  25us -> 500us.