Merge branch 'ftrace-bpf-use-single-direct-ops-for-bpf-trampolines'

Merge branch 'ftrace-bpf-use-single-direct-ops-for-bpf-trampolines'

Jiri Olsa says:

====================
ftrace,bpf: Use single direct ops for bpf trampolines

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/20250729102813.1531457-1-jolsa@kernel.org/
v1:  https://lore.kernel.org/bpf/20250923215147.1571952-1-jolsa@kernel.org/
v2:  https://lore.kernel.org/bpf/20251113123750.2507435-1-jolsa@kernel.org/
v3:  https://lore.kernel.org/bpf/20251120212402.466524-1-jolsa@kernel.org/
v4:  https://lore.kernel.org/bpf/20251203082402.78816-1-jolsa@kernel.org/
v5:  https://lore.kernel.org/bpf/20251215211402.353056-10-jolsa@kernel.org/

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]

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/20251027175023.1521602-1-song@kernel.org/
[2] https://lore.kernel.org/bpf/20250924050415.4aefcb91@batman.local.home/
---
====================

Link: https://patch.msgid.link/20251230145010.103439-1-jolsa@kernel.org
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>