I have a test case similar to code in xdp-project/xdp-tutorial/ which maintains a statistic map in a per-cpu array, and user-space code which displays the statistics periodically. When I run this, the user space code always displays zeros. I have instrumented my eBPF kernel code with bpf_trace_printk and it appears to be putting the correct values into the map. The user code is iterating over all possible CPUs, but is always finding zeros in the per-cpu array slots. Can anybody tell me what is going wrong ? My test case is here https://github.com/tjcw/bpf-examples/tree/tjcw-integration-1.2-ebpftrace/AF_XDP-filter ; af_xdp_kern.c is the eBPF code, af_xdp_user.c is the userspace code which drives the eBPF code, and filter-xdp_stats.c is the code which should display the statistics. It all builds with 'make' in that directory, and there is a run script which I use with tjcw@r28b29-n10:~/workspace/bpf-examples/AF_XDP-filter/netperf-namespace$ sudo FILTER=af_xdp_kern ./run.sh to run the user code and eBPF code with data being transferred between 2 network namespaces on the machine. While it is running, tjcw@r28b29-n10:~/workspace/bpf-examples/AF_XDP-filter$ sudo ./filter-xdp_stats should display statistics, but in fact displays zeros. My test case is coded to the '1.0' BPF interface, where the code in xdp-tutorial is coded to the pre-release BPF interface. Thanks for all the help you can give ! Chris Ward, IBM
