• Marc Zyngier's avatar
    KVM: arm/arm64: timer: Add active state caching · 9b4a3004
    Marc Zyngier authored
    Programming the active state in the (re)distributor can be an
    expensive operation so it makes some sense to try and reduce
    the number of accesses as much as possible. So far, we
    program the active state on each VM entry, but there is some
    opportunity to do less.
    An obvious solution is to cache the active state in memory,
    and only program it in the HW when conditions change. But
    because the HW can also change things under our feet (the active
    state can transition from 1 to 0 when the guest does an EOI),
    some precautions have to be taken, which amount to only caching
    an "inactive" state, and always programing it otherwise.
    With this in place, we observe a reduction of around 700 cycles
    on a 2GHz GICv2 platform for a NULL hypercall.
    Reviewed-by: default avatarChristoffer Dall <christoffer.dall@linaro.org>
    Signed-off-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
arm_arch_timer.h 2.3 KB