[Qemu-devel] deterministic qemu

[Qemu-devel] deterministic qemu

[Steven Seeger]

I wanted to update the list on my progress and a follow-up of the "ppc and 
icount" thread.

The issue I was seeing is the case where an io memory write triggers a timer 
value to be set. In single-thread TCG, timers are run in 
handle_icount_deadline() and once that's done, TBs are executed. Since cpu-
>icount_budget is 5000000 (icount==3), a timer being set to 88 microseconds 
will fire way late. This caused the tremendous slowdown I was seeing during 
the start of my binary when the vxWorks bootup banner came up. I have a simple 
fix for this (set cpu->exit_request=1 in qemu_start_warp_timer, a total hack) 
but I'm sure that's not "correct."

The other thing is -icount 3,align=on makes it run correctly assuming the host 
can keep up.

The end result is every time I run my executable I get the same virtual clock 
value for some given event. I'm very happy.

I still don't have a fix for the issue in commit 
044897ef4a22af89aecb8df509477beba0a2e0ce but I reverted it and things are 
working for me.

Steven