• Jason Wang's avatar
    vhost: introduce O(1) vq metadata cache · f8894913
    Jason Wang authored
    When device IOTLB is enabled, all address translations were stored in
    interval tree. O(lgN) searching time could be slow for virtqueue
    metadata (avail, used and descriptors) since they were accessed much
    often than other addresses. So this patch introduces an O(1) array
    which points to the interval tree nodes that store the translations of
    vq metadata. Those array were update during vq IOTLB prefetching and
    were reset during each invalidation and tlb update. Each time we want
    to access vq metadata, this small array were queried before interval
    tree. This would be sufficient for static mappings but not dynamic
    mappings, we could do optimizations on top.
    
    Test were done with l2fwd in guest (2M hugepage):
    
       noiommu  | before        | after
    tx 1.32Mpps | 1.06Mpps(82%) | 1.30Mpps(98%)
    rx 2.33Mpps | 1.46Mpps(63%) | 2.29Mpps(98%)
    
    We can almost reach the same performance as noiommu mode.
    Signed-off-by: default avatarJason Wang <[email protected]>
    Signed-off-by: default avatarMichael S. Tsirkin <[email protected]>
    f8894913
vhost.c 59.2 KB