some issues with the current Debian snapshot

[perkelix]

Linux u1400 6.12.90+deb13-pentium4 #1 SMP PREEMPT_DYNAMIC Sun May 24 08:58:08 EEST 2026 i686 GNU/Linux

bpftune  0.0~git20251206.4bcc284-1

Jun 18 09:29:01 u1400 systemd[1]: Started bpftune.service - BPF-based auto-tuning of system parameters.
Jun 18 09:29:04 u1400 bpftune[894]: bpftune works in legacy mode
Jun 18 09:29:04 u1400 bpftune[894]: bpftune does not support per-netns policy (via netns cookie)
Jun 18 09:29:04 u1400 bpftune[894]: error initializing '/usr/lib/i386-linux-gnu/bpftune//netns_tuner.so: Operation not supported
Jun 18 09:29:09 u1400 bpftune[894]: error initializing '/usr/lib/i386-linux-gnu/bpftune//udp_buffer_tuner.so: Operation not supported
Jun 18 09:29:13 u1400 bpftune[894]: could not attach skeleton: No such file or directory
Jun 18 09:29:57 u1400 bpftune[894]: BPF load for tuner 'tcp_conn; failed: 'Permission denied':
Jun 18 09:29:57 u1400 bpftune[894]: error initializing '/usr/lib/i386-linux-gnu/bpftune//tcp_conn_tuner.so: Permission denied
Jun 18 09:29:58 u1400 bpftune[894]: error initializing '/usr/lib/i386-linux-gnu/bpftune//netns_tuner.so: Operation not supported
Jun 18 09:30:01 u1400 bpftune[894]: error initializing '/usr/lib/i386-linux-gnu/bpftune//udp_buffer_tuner.so: Operation not supported
Jun 18 09:30:04 u1400 bpftune[894]: could not attach skeleton: No such file or directory
Jun 18 09:30:07 u1400 bpftune[894]: BPF load for tuner 'tcp_conn; failed: 'Permission denied':
Jun 18 09:30:07 u1400 bpftune[894]: error initializing '/usr/lib/i386-linux-gnu/bpftune//tcp_conn_tuner.so: Permission denied

[alan-maguire]

could you try running bpftune with verbose output (from the commandline sudo bpftune -ds )? thanks!

[perkelix]

Attached. bpftune_ds.txt

[alan-maguire]

thanks! first issue:

bpftune: libbpf: map 'probe_bp.bss': created successfully, fd=11
bpftune: libbpf: prog 'probe_cong_iter': BPF program load failed: -EACCES
bpftune: libbpf: prog 'probe_cong_iter': -- BEGIN PROG LOAD LOG --
0: R1=ctx() R10=fp0
; struct sock_common *skc = ctx->sk_common; @ probe.bpf.c:40
0: (61) r1 = *(u32 *)(r1 +8)
func 'bpf_iter_tcp' size 4 must be 8
invalid bpf_context access off=8 size=4
processed 1 insns (limit 1000000) max_states_per_insn 0 total_states 0 peak_states 0 mark_read 0
-- END PROG LOAD LOG --

This probe failing makes us believe we are not able to fully support BPF, which has cascading effects on other tuners.

The immediate cause is the BPF program thinks skc (a pointer) should be size 4, while BTF tells us it is 8. Why?

Looking at the logs we are running

Jun 18 09:29:04 u1400 bpftune[894]: error initializing '/usr/lib/i386-linux-gnu/bpftune//netns_tuner.so: Operation not supported

i.e. this is 32-bit bpftune. bpftune is currently not supported for 32-bit.

[perkelix]

Is there any particular reason for hard-coding 64-bit assumptions?

[alan-maguire]

two reasons - limited resources and complexity. bpf is a bit of a strange bird in that we have code that looks like userspace code (BPF code) that runs in-kernel so has to match the kernel ISA. dealing with the permutations is as a result quite tricky.