From: Jason Wang <jasowang@xxxxxxxxxx> Date: Tue, 9 Jan 2018 18:27:45 +0800 > This patch tries to batched used ring update during RX. This is pretty > fit for the case when guest is much faster (e.g dpdk based > backend). In this case, used ring is almost empty: > > - we may get serious cache line misses/contending on both used ring > and used idx. > - at most 1 packet could be dequeued at one time, batching in guest > does not make much effect. > > Update used ring in a batch can help since guest won't access the used > ring until used idx was advanced for several descriptors and since we > advance used ring for every N packets, guest will only need to access > used idx for every N packet since it can cache the used idx. To have a > better interaction for both batch dequeuing and dpdk batching, > VHOST_RX_BATCH was used as the maximum number of descriptors that > could be batched. > > Test were done between two machines with 2.40GHz Intel(R) Xeon(R) CPU > E5-2630 connected back to back through ixgbe. Traffic were generated > on one remote ixgbe through MoonGen and measure the RX pps through > testpmd in guest when do xdp_redirect_map from local ixgbe to > tap. RX pps were increased from 3.05 Mpps to 4.00 Mpps (about 31% > improvement). > > One possible concern for this is the implications for TCP (especially > latency sensitive workload). Result[1] does not show obvious changes > for most of the netperf test (RR, TX, and RX). And we do get some > improvements for RX on some specific size. ... > Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx> Applied, thanks Jason.
