On 26/06/2015 20:07, Dr. David Alan Gilbert wrote:
* Jason J. Herne (address@hidden) wrote:
Provide a method to throttle guest cpu execution. CPUState is augmented with
timeout controls and throttle start/stop functions. To throttle the guest cpu
the caller simply has to call the throttle set function and provide a percentage
of throttle time.
I'm worried about atomicity and threads and all those fun things.
I think all the starting/stopping/setting the throttling level is done in the
migration thread; I think the timers run in the main/io thread?
So you really need to be careful with at least:
throttle_timer_stop - which may have a minor effect
throttle_timer - I worry about the way cpu_timer_active checks the pointer
yet it's freed when the timer goes off. It's probably
not too bad because it never dereferences it.
Agreed. I think the only atomic should be throttle_percentage; if zero,
throttling is inactive.
In particular, throttle_ratio can be computed in cpu_throttle_thread.
If you have exactly one variable that is shared between the threads,
everything is much simpler.
There is no need to allocate and free the timer; it's very cheap and in
fact we probably should convert to statically allocated timers sooner or
later. So you can just create it once, for example in cpu_ticks_init.