On Thu, 10 May 2018 15:35:59 +0700 Naruto Nguyen <narutonguyen2...@gmail.com> wrote:
> Hello everyone, > > Recently, I used netperf to test the TCP performance on loopback > interface on my 2 nodes, one is installed kernel 4.4.103 and the other > is 3.12.61 > > netperf -l 100 -t TCP_RR > netperf -l 100 -t TCP_RR -- -D > > In both cases, I see that the throughput on 4.4.103 is about just 1/2 > in comparing with 3.12.61 node > > # netperf -l 100 -t TCP_RR > MIGRATED TCP REQUEST/RESPONSE TEST from 0.0.0.0 (0.0.0.0) port 0 > AF_INET to localhost () port 0 AF_INET : first burst 0 > Local /Remote > Socket Size Request Resp. Elapsed Trans. > Send Recv Size Size Time Rate > bytes Bytes bytes bytes secs. per sec > > 16384 87380 1 1 100.00 37714.68 > 16384 87380 > > > netperf -l 100 -t TCP_RR > MIGRATED TCP REQUEST/RESPONSE TEST from 0.0.0.0 (0.0.0.0) port 0 > AF_INET to localhost () port 0 AF_INET : first burst 0 > Local /Remote > Socket Size Request Resp. Elapsed Trans. > Send Recv Size Size Time Rate > bytes Bytes bytes bytes secs. per sec > > 16384 87380 1 1 100.00 64038.41 > 16384 87380 > > > When running tcpdump to capture all packets in loopback interface, I > see that during 200s capture, the number of packets on loopback of > 4.4.103 is double the number of packets in 3.12.61? Could you please > let me know if it can cause the low throughput as above? Do we have > any tuning for TCP on loopback to improve the performace (actually the > low throughput also happens with UDP) or if we have any known > performance issue in 4.4 kernel on loopback? > > Thanks a lot, > Brs, > Naruto This might just be the increased overhead of KPTI to fix Spectre/Meltdown. Loopback is very sensitive to syscall overhead.
