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I found this issue while adding sched_ext support for > LoongArch. When scx_bpf_create_dsq() failed during my development, there > were no error messages at all, which made debugging difficult. > > Specifically: > 1. The failure was silent - no log, no error message in dmesg Which kernel is that? In theory you should get a clear message in dmesg. For example, if I try to create an invalid DSQ in scx_simple I get this in dmesg: [690301.673313] sched_ext: BPF scheduler "simple" disabled (runtime error) [690301.673324] sched_ext: simple: ops.init() failed (-22) [690301.673327] scx_enable.isra.0+0xc8b/0x11f0 [690301.673343] bpf_struct_ops_link_create+0x141/0x1b0 [690301.673352] __sys_bpf+0x1c0c/0x2de0 [690301.673357] __x64_sys_bpf+0x21/0x30 [690301.673359] do_syscall_64+0x81/0x820 [690301.673368] entry_SYSCALL_64_after_hwframe+0x76/0x7e And in stdout: DEBUG DUMP ================================================================================ scx_simple[364999] triggered exit kind 1024: runtime error (ops.init() failed (-22)) Backtrace: scx_enable.isra.0+0xc8b/0x11f0 bpf_struct_ops_link_create+0x141/0x1b0 __sys_bpf+0x1c0c/0x2de0 __x64_sys_bpf+0x21/0x30 do_syscall_64+0x81/0x820 entry_SYSCALL_64_after_hwframe+0x76/0x7e CPU states ---------- CPU 2 : nr_run=0 flags=0x1 cpu_rel=0 ops_qseq=87907495 pnt_seq=66861592 curr=scx_simple[364999] class=fair_sched_class CPU 3 : nr_run=0 flags=0x1 cpu_rel=0 ops_qseq=85461608 pnt_seq=64229201 curr=pacman[364201] class=fair_sched_class Event counters -------------- SCX_EV_SELECT_CPU_FALLBACK: 0 SCX_EV_DISPATCH_LOCAL_DSQ_OFFLINE: 0 SCX_EV_DISPATCH_KEEP_LAST: 0 SCX_EV_ENQ_SKIP_EXITING: 0 SCX_EV_ENQ_SKIP_MIGRATION_DISABLED: 0 SCX_EV_REFILL_SLICE_DFL: 0 SCX_EV_BYPASS_DURATION: 0 SCX_EV_BYPASS_DISPATCH: 0 SCX_EV_BYPASS_ACTIVATE: 0 ================================================================================ EXIT: runtime error (ops.init() failed (-22)) > 2. I had to add bpf_printk() temporarily to confirm it was dsq creation failing > > So the benefit is improved debuggability and faster issue diagnosis. > > Thanks! > Thanks, -Andrea