Re: [Qemu-devel] [PATCH v2 0/9] target-arm: EL3 trap support

[Edgar E. Iglesias]

---
Sent from my phone
On 23/04/2015 8:10 pm, "Peter Maydell" <address@hidden> wrote:
>
> On 23 April 2015 at 04:37, Edgar E. Iglesias <address@hidden> wrote:
> > I had a comment on the trapping of WFX, I recall not checking for
> > has_work was causing a lot of exception round-trips when running
> > XEN. To the point were things almost stopped working.
>
> For traps on WFE, or traps on WFI? If the former, we should
> probably implement that as "never trap" since we don't actually
> go into a 'low power state' for WFE (execution will always
> continue even if there's no pending WFE event).
>
> -- PMM

Hi,

I think it was for both, I can retest it to double check.

Our (xilinx) tree tracks wfe wakeups.

I agree that without tracking we better not trap..

When running emulated SMP with multiple nested SMP guests there are a lot of these events fired. The exception code paths down to hypervisors involve fairly long round trips.

Cheers,
Edgar