VT-x causes massive DPC latency

[maqr]

I am running Windows 7 x64 on a q6600 with virtualization enabled in the bios. Whenever my guest (x64 or x86) is under any kind of load (even just booting the Ubuntu installer), I get big DPC latency spikes. This is obviously a problem because it causes choppy audio, video, and generally degrades performance. Once inside the guest OS, this is can be easily reproduced with a simple bash script: while true; do ""; done

I have reproduced this on an i7 920 with the same problem.

Attached is a dpclat screenshot and a dump from xperf. If the ETL would be beneficial in debugging, I could produce one.

The "fix" for me was to install a 32-bit guest and disable VT-x in the vbox options.

[maqr]

DPClat screenshot

[maqr]

Summary from xperf

[Craig Mason]

I just assumed that the jumping issues were normal behaviour. When I run with 2 cores and VT-x (especially when running a 64-bit OS) I get audio choppiness, mouse juddering, and a whole host of other host and guest based performance issues.

[Frank Mehnert]

Yes, this behavior is possible with Windows 7 / x64 and there is already a fix in the trunk. Not sure if the next version or the version after the next version will contain the fix.

[Frank Mehnert]

Should be fixed in VBox 3.2 (IIRC) and VBox 4.0.

[gijs]

im also having quite high dpc latency's with the latest virtual box 4.0.8 this happens under a powerful machine.

I have made a post on the forums already, which describes everything: ​http://forums.virtualbox.org/viewtopic.php?f=6&t=38561

[Frank Mehnert]

The posting is not 100% clear: What is your host, Windows Server 2003 r2? Or is that your guest?

[gijs]

host is windows 7 64 bit(now with sp1), the guest is server 2003 r2 32 bit. I have also tried as guest windows 7 sp1 32 bit, it has the same issue.

ill try a 64 bit guest soon.

[gijs]

I tried server 2008 r2(64 bit) as a guest os, the dpc latency might have been a bit lower bit it was still on the high side and this was idle with a clean install.

[gijs]

oh btw im running dpc latency checker on the host os.

[Frank Mehnert]

Should be improved with VBox 4.3.4.

[tk-oracle]

I just want to confirm that this problem is gone on my Windows 7 64 Bit system. I have been just looking for the reason of the DPC latency, which I found on my system. After upgrading to Version 4.3.4 it is gone. Thanks a lot.

[JosefCarlin]

I also had this problem and it immediately went away after installing 4.3.4. I checked the changelog and found this report. In my case I was using Win7Ultimate 64-bit host with various 32/64 bit guests (WinXP 32/64-bit, OEL 64-bit, RHEL 32/64-bit, Centos 32/64-bit). The host has a Intel Core 2 Quad CPU Q9550 @ 2.83GHz and 8 GB of memory. Typically I allocate 2 cores and 2GB to the VM's. The audio/video streams were to Windows Media Center from a Hauppauge HD PVR Tuner and Realteck High Definition Audio devices. Symptoms included choppy audio and video which "creeped" into the playback after 30 minutes or so.

[Frank Mehnert]

Thank you for the feedback. I will close this ticket as further improvements are not to be expected.