Re: [PATCH RESEND 5/9] hw/arm/smmuv3: Store the starting level in SMMUTransTableInfo

[Peter Maydell]

On Thu, 11 Jun 2020 at 17:15, Eric Auger <eric.auger@redhat.com> wrote:
>
> Compute the starting level on CD decoding and store it
> into SMMUTransTableInfo. We will need this information
> on IOTLB lookup so let's avoid to recompute it each time.
>
> Signed-off-by: Eric Auger <eric.auger@redhat.com>

> --- a/hw/arm/smmu-common.c
> +++ b/hw/arm/smmu-common.c
> @@ -224,7 +224,7 @@ static int smmu_ptw_64(SMMUTransCfg *cfg,
>      granule_sz = tt->granule_sz;
>      stride = granule_sz - 3;
>      inputsize = 64 - tt->tsz;
> -    level = 4 - (inputsize - 4) / stride;
> +    level = tt->starting_level;

"4 - (x - 4) / y" doesn't really seem like it's complicated
enough to be worth caching given everything else we do on
a page table walk. Do you have perf figures to indicate that
this change is worthwhile?

thanks
-- PMM