Re: [Qemu-devel] [PATCH v2 9/9] target-arm: Add WFx instruction trap support

[Greg Bellows]

On Thu, Apr 23, 2015 at 9:51 AM, Peter Maydell <address@hidden> wrote:

On 23 April 2015 at 15:41, Greg Bellows <address@hidden> wrote:
> Ok it sounds like the primary concern is the performance impact of
> constantly trapping wfe to EL2 (in which case HCR must be set to cause
> this).  Should we still honor EL3 and EL1 trapping ofr wfe?  In other words
> check if they are the target and allow it if !has_work?

We should check what the architecture manual says, but I think
that in all the trap-WFE cases it says "traps if the CPU
would go into a low power state". QEMU *never* goes into a
low power state on WFE, so we never trap.

​Right, that is exactly what it says.  So if QEMU never goes into a low power state than neither wfi or wfe should trap as they have the same explanation. In which case the best solution is to pull the patches out.  That work?

 

-- PMM