[vbox-dev] Driver ISR call delayed for device interrupts

Michal Necasek michal.necasek at oracle.com
Wed Jun 15 07:49:56 UTC 2016

     Hi Vic,

  It probably does not hurt to state that if you require real-time 
responsiveness, you should *not* be using a VM. There are no latency 

  You forgot to mention the most relevant fact... which svn revision of 
the OSE source code are you actually using? In fact you expect any kind 
of technical support, you might as well start by providing a VBox.log 
because all the information is in there.

  How exactly do you measure the delay? I assume it's from the device 
calling PDMDevHlpPCISetIrq to the guest accessing some device register 
in the ISR?

  There might be problems specific to Windows 8.1(?) hosts. If you could 
repeat the test on a different host OS (ideally not Windows), that might 
provide some hints.

  I don't know of anything in particular that would happen every 500 ms 
in VirtualBox, but it doesn't have to be the VM, it could be the host 
doing something as well.


On 6/15/2016 8:51 AM, llyzs wrote:
> Hi Devs,
> I have a virtual PCI device added on VirtualBox OSE and a driver which
> sends I/O to do some stuff in the host and receive interrupts when the
> work is done. The interrupts work most of the time, however there are
> random delays between PDMDevHlpPCISetIrq is called and the driver ISR is
> called. Most of the time there is no delay (<1ms) but periodically there
> is a delay from 10+ms to even 60+ms. One more strange thing is that the
> delay mostly happen at exactly every 500ms. So anyone can give me some
> hint on what is causing the interrupt delay? What kind of job inside
> VirtualBox that runs every 500ms that might be causing interrupt delay?
> I am on Windows 8.1 x64 (both guest and host). Thanks in advanced.
> Vic
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