On Thu, 2 Jul 2020 at 16:27, Eric Auger <eric.au...@redhat.com> wrote: > > Instead of using a Jenkins hash function to generate > the key let's just use a 64 bit unsigned integer that > contains the asid and the 40 upper bits of the iova. > A maximum of 52-bit IOVA is supported. This change in the > key format also prepares for the addition of new fields > in subsequent patches (granule and level). > > Signed-off-by: Eric Auger <eric.au...@redhat.com>
> diff --git a/hw/arm/smmu-common.c b/hw/arm/smmu-common.c > index 7dc8541e8b..5e85e30bdf 100644 > --- a/hw/arm/smmu-common.c > +++ b/hw/arm/smmu-common.c > @@ -34,34 +34,17 @@ > > static guint smmu_iotlb_key_hash(gconstpointer v) > { > - SMMUIOTLBKey *key = (SMMUIOTLBKey *)v; > - uint32_t a, b, c; > - > - /* Jenkins hash */ > - a = b = c = JHASH_INITVAL + sizeof(*key); > - a += key->asid; > - b += extract64(key->iova, 0, 32); > - c += extract64(key->iova, 32, 32); > - > - __jhash_mix(a, b, c); > - __jhash_final(a, b, c); > - > - return c; > + return (guint)*(const uint64_t *)v; > } So the hash value is now going to be the lower 32 bits of the key, which is to say bits [40,12] of the IOVA, and won't include the ASID at all. Isn't that going to result in more hash collisions than would be ideal? I was going to suggest using the glib builtin g_int64_hash() instead, but looking at the source that seems to be the identical implementation to this one. I guess that's intended for cases where an integer key is really a random integer, not one where it's got internal structure of different bit fields within it being for different purposes. thanks -- PMM