XEN 4.11 PV questions

[Asaf Fisher <asaffisher.dev@xxxxxxxxx>]

Hello,

In general I have a intel family 6 model 94 and xen does not support so I want to add support to it.

For the question:

I’m trying to understand exactly how and when dom0’s vCPU gets a runtime and where in the code is like the “vmenter”(I know there is no such a thing in pv..) 

So:

1. I got 2 pCPUs and I see that after the secondary cpu gets setup it goes into and idle loop and wait for a task. 

2. When primary cpu finishes init xen, it unpauses dom0 and therefore schedule it’s vCPU and call the wake function on the credit scheduler.

I’m getting a hard time understanding what the wake do... does it put a tasklet in the percpu section and then the pCPU see it in its tasklet on the idle loop? If not what really happens? If yes, how what is the code flow that causes the dom0 code to be executed? Is it a context switch? If so where? Or is it just a function call?(I think it’s highly unlikely) 

Another hypothesis of mine is that the tasklet is just for callbacks and not for guests? And do_softirq actually causes scheduling and eventually causes the cpu to run dom0? I REALLY want to know where the hell is the last line before a cpu gets into the dom0 context xD 

Thanks! I will appreciate the help so much!