On Thu, Apr 23, 2015 at 6:34 AM, Edgar E. Iglesias <edgar.igles...@gmail.com > wrote:
> On Thu, Apr 23, 2015 at 12:28:43PM +0100, Peter Maydell wrote: > > On 23 April 2015 at 12:24, Edgar E. Iglesias <edgar.igles...@gmail.com> > wrote: > > > Maybe we can consider YIELD instead of NOP when has_work() is true as > a WFI > > > is probably a good hint from guests to reschedule QEMU CPUs. > > > > That I'm not convinced about. If we have a pending interrupt then > > our best bet is probably to take it immediately on this CPU, not > > yield to another CPU and take the interrupt when we eventually > > get control back. > > Yeah, true. It's actually a very bad YIELD point when has_work() is true > for a WFI. > > For WFE too I guess, when interrupts are unmasked. > > Good point. > > Cheers, > Edgar > Good catch Edgar, we shouldn't trap if we are "going into a low-power state". It sounds like we arrived at the following: wfi- check has_work before taking either the UDEF or HLT exception hereby making it a noop. wfe - Never trap, making it always a noop. This includes undoing the existing YIELD exception. Sound right?
