On Thu, Dec 13, 2018 at 06:10:19PM +0800, Jason Wang wrote: > Hi: > > This series tries to access virtqueue metadata through kernel virtual > address instead of copy_user() friends since they had too much > overheads like checks, spec barriers or even hardware feature > toggling. > > Test shows about 24% improvement on TX PPS. It should benefit other > cases as well. > > Please review I think the idea of speeding up userspace access is a good one. However I think that moving all checks to start is way too aggressive. Instead, let's batch things up but let's not keep them around forever. Here are some ideas: 1. Disable preemption, process a small number of small packets directly in an atomic context. This should cut latency down significantly, the tricky part is to only do it on a light load and disable this for the streaming case otherwise it's unfair. This might fail, if it does just bounce things out to a thread. 2. Switch to unsafe_put_user/unsafe_get_user, and batch up multiple accesses. 3. Allow adding a fixup point manually, such that multiple independent get_user accesses can get a single fixup (will allow better compiler optimizations). > Jason Wang (3): > vhost: generalize adding used elem > vhost: fine grain userspace memory accessors > vhost: access vq metadata through kernel virtual address > > drivers/vhost/vhost.c | 281 ++++++++++++++++++++++++++++++++++++++---- > drivers/vhost/vhost.h | 11 ++ > 2 files changed, 266 insertions(+), 26 deletions(-) > > -- > 2.17.1
