Brad Campbell | 1 Aug 13:17 2006

Re: Run Real Time Guest OS?

Steve Ellenoff wrote:
> Is it possible to run a real time OS under qemu? What changes would need 
> to be made?
> Can it even be done?
> The guest OS I'm trying to run sets the RTC System Timer 0 to a 0.25ms 
> interval (~4000Hz)!! The program I'm trying to run on it, expects this 
> time to be accurate, and as such, visually the program seems to be 4-5x 
> too slow in qemu, which makes sense given that it's delivering only a 
> 1024Hz timer irq.
> I've noticed in the source code that qemu sets this max value of 1024Hz 
> (1ms) for the timer, which from what I understand is a limit of the 
> Linux kernel itself, ie, that's the most the kernel can support.
Not at all.. for a single qemu instance on linux it tries to use the PIT in the rtc, and I've seen 
this run upto 8192hz. Why not crank it up in the qemu source t0 4096 and see what happens. It's not 
going to hurt anything in any case.
You would most certainly want a HZ value of 1000 to try this.


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