On Tue, 11 Jul 2017 12:37:10 -0700 John Fastabend <john.fastab...@gmail.com> wrote:
> > I have a really strange observation... if I change the CPU powersave > > settings, then the xdp_redirect_map performance drops in half! Above > > was with "tuned-adm profile powersave" (because, this is a really noisy > > server, and I'm sitting next to it). I can see that the CPU under-load > > goes into "turbomode", rest going into low-power, including the > > Hyper-thread siblings. > > > > If I change the profile to: # tuned-adm profile network-latency > > > > ifindex 6: 12964879 pkt/s > > ifindex 6: 12964683 pkt/s > > ifindex 6: 12961497 pkt/s > > ifindex 6: 11779966 pkt/s <-- change to tuned-adm profile network-latency > > ifindex 6: 6853959 pkt/s > > ifindex 6: 6851120 pkt/s > > ifindex 6: 6856934 pkt/s > > ifindex 6: 6857344 pkt/s > > ifindex 6: 6857161 pkt/s > > > > The CPU efficiency goes from 2.35 to 1.24 insn per cycle. > > > > John do you know some Intel people that could help me understand what > > is going on?!? This is very strange... > > > > I tried Andi's toplev tool, which AFAIK indicate that this is a > > Frontend problem, e.g. in decoding the instructions?!? > > > > hmm maybe Jesse or Alex have some clues. Adding them to the CC list. This seems related to Hyper-Threading. I tried to disable hyperthreading in the BIOS, and the problem goes away. That is, the benchmarks are no-longer affected by the CPU tuned-adm profile. -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer
