On Tue, Dec 30, 2025 at 6:50 AM Jiri Olsa <[email protected]> wrote: > > hi, > while poking the multi-tracing interface I ended up with just one ftrace_ops > object to attach all trampolines. > > This change allows to use less direct API calls during the attachment changes > in the future code, so in effect speeding up the attachment. > > In current code we get a speed up from using just a single ftrace_ops object. > > - with current code: > > Performance counter stats for 'bpftrace -e fentry:vmlinux:ksys_* {} -c > true': > > 6,364,157,902 cycles:k > 828,728,902 cycles:u > 1,064,803,824 instructions:u # 1.28 insn per > cycle > 23,797,500,067 instructions:k # 3.74 insn per > cycle > > 4.416004987 seconds time elapsed > > 0.164121000 seconds user > 1.289550000 seconds sys > > > - with the fix: > > Performance counter stats for 'bpftrace -e fentry:vmlinux:ksys_* {} -c > true': > > 6,535,857,905 cycles:k > 810,809,429 cycles:u > 1,064,594,027 instructions:u # 1.31 insn per > cycle > 23,962,552,894 instructions:k # 3.67 insn per > cycle > > 1.666961239 seconds time elapsed > > 0.157412000 seconds user > 1.283396000 seconds sys > > > > The speedup seems to be related to the fact that with single ftrace_ops object > we don't call ftrace_shutdown anymore (we use ftrace_update_ops instead) and > we skip the synchronize rcu calls (each ~100ms) at the end of that function. > > rfc: https://lore.kernel.org/bpf/[email protected]/ > v1: https://lore.kernel.org/bpf/[email protected]/ > v2: https://lore.kernel.org/bpf/[email protected]/ > v3: https://lore.kernel.org/bpf/[email protected]/ > v4: https://lore.kernel.org/bpf/[email protected]/ > v5: https://lore.kernel.org/bpf/[email protected]/ > > v6 changes: > - rename add_hash_entry_direct to add_ftrace_hash_entry_direct [Steven] > - factor hash_add/hash_sub [Steven] > - add kerneldoc header for update_ftrace_direct_* functions [Steven] > - few assorted smaller fixes [Steven] > - added missing direct_ops wrappers for > !CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS > case [Steven] >
So this looks good from BPF side, I think. Steven, if you don't mind giving this patch set another look and if everything is to your liking giving your ack, we can then apply it to bpf-next. Thanks! > v5 changes: > - do not export ftrace_hash object [Steven] > - fix update_ftrace_direct_add new_filter_hash leak [ci] > > v4 changes: > - rebased on top of bpf-next/master (with jmp attach changes) > added patch 1 to deal with that > - added extra checks for update_ftrace_direct_del/mod to address > the ci bot review > > v3 changes: > - rebased on top of bpf-next/master > - fixed update_ftrace_direct_del cleanup path > - added missing inline to update_ftrace_direct_* stubs > > v2 changes: > - rebased on top fo bpf-next/master plus Song's livepatch fixes [1] > - renamed the API functions [2] [Steven] > - do not export the new api [Steven] > - kept the original direct interface: > > I'm not sure if we want to melt both *_ftrace_direct and the new interface > into single one. It's bit different in semantic (hence the name change as > Steven suggested [2]) and I don't think the changes are not that big so > we could easily keep both APIs. > > v1 changes: > - make the change x86 specific, after discussing with Mark options for > arm64 [Mark] > > thanks, > jirka > > > [1] https://lore.kernel.org/bpf/[email protected]/ > [2] https://lore.kernel.org/bpf/[email protected]/ > --- > Jiri Olsa (9): > ftrace,bpf: Remove FTRACE_OPS_FL_JMP ftrace_ops flag > ftrace: Make alloc_and_copy_ftrace_hash direct friendly > ftrace: Export some of hash related functions > ftrace: Add update_ftrace_direct_add function > ftrace: Add update_ftrace_direct_del function > ftrace: Add update_ftrace_direct_mod function > bpf: Add trampoline ip hash table > ftrace: Factor ftrace_ops ops_func interface > bpf,x86: Use single ftrace_ops for direct calls > > arch/x86/Kconfig | 1 + > include/linux/bpf.h | 7 ++- > include/linux/ftrace.h | 31 +++++++++- > kernel/bpf/trampoline.c | 259 > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--------------- > kernel/trace/Kconfig | 3 + > kernel/trace/ftrace.c | 406 > +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-------- > 6 files changed, 632 insertions(+), 75 deletions(-) >
