Re: [Qemu-arm] [Qemu-devel] [PATCH 04/19] nvic: Add cached vectpending_prio state

[Richard Henderson]

On 09/12/2017 11:13 AM, Peter Maydell wrote:
> Instead of looking up the pending priority
> in nvic_pending_prio(), cache it in a new state struct
> field. The calculation of the pending priority given
> the interrupt number is more complicated in v8M with
> the security extension, so the caching will be worthwhile.
> 
> This changes nvic_pending_prio() from returning a full
> (group + subpriority) priority value to returning a group
> priority. This doesn't require changes to its callsites
> because we use it only in comparisons of the form
>   execution_prio > nvic_pending_prio()
> and execution priority is always a group priority, so
> a test (exec prio > full prio) is true if and only if
> (execprio > group_prio).
> 
> (Architecturally the expected comparison is with the
> group priority for this sort of "would we preempt" test;
> we were only doing a test with a full priority as an
> optimisation to avoid the mask, which is possible
> precisely because the two comparisons always give the
> same answer.)
> 
> Signed-off-by: Peter Maydell <address@hidden>
> ---
>  include/hw/intc/armv7m_nvic.h |  2 ++
>  hw/intc/armv7m_nvic.c         | 23 +++++++++++++----------
>  hw/intc/trace-events          |  2 +-
>  3 files changed, 16 insertions(+), 11 deletions(-)

Reviewed-by: Richard Henderson <address@hidden>


r~