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.
I got following speed up when measuring simple attach/detach 300 times [1].
- with current code:
perf stat -e cycles:k,cycles:u,instructions:u,instructions:k -- ./test_progs -t krava -w0
#158 krava:OK
Summary: 1/0 PASSED, 0 SKIPPED, 0 FAILED
Performance counter stats for './test_progs -t krava -w0':
12,003,420,519 cycles:k
63,239,794 cycles:u
102,155,625 instructions:u # 1.62 insn per cycle
11,614,183,764 instructions:k # 0.97 insn per cycle
35.448142362 seconds time elapsed
0.011032000 seconds user
2.478243000 seconds sys
- with the fix:
perf stat -e cycles:k,cycles:u,instructions:u,instructions:k -- ./test_progs -t krava -w0
#158 krava:OK
Summary: 1/0 PASSED, 0 SKIPPED, 0 FAILED
Performance counter stats for './test_progs -t krava -w0':
14,327,218,656 cycles:k
46,285,275 cycles:u
102,125,592 instructions:u # 2.21 insn per cycle
14,620,692,457 instructions:k # 1.02 insn per cycle
2.860883990 seconds time elapsed
0.009884000 seconds user
2.777032000 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 300 synchronize rcu calls (each ~100ms) at the end of that function.
v1 changes:
- make the change x86 specific, after discussing with Mark options for
arm64 [Mark]
thanks,
jirka
[1] https://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git/commit/?h=test&id=1b7fc74c36a93e90816f58c37a84522f0949095a
---
Jiri Olsa (9):
ftrace: Make alloc_and_copy_ftrace_hash direct friendly
ftrace: Add register_ftrace_direct_hash function
ftrace: Add unregister_ftrace_direct_hash function
ftrace: Add modify_ftrace_direct_hash function
ftrace: Export some of hash related functions
ftrace: Use direct hash interface in direct functions
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 | 48 ++++++++++---
kernel/bpf/trampoline.c | 128 +++++++++++++++++++++++++--------
kernel/trace/Kconfig | 3 +
kernel/trace/ftrace.c | 477 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++---------------------------------------------
kernel/trace/trace.h | 8 ---
kernel/trace/trace_selftest.c | 5 +-
8 files changed, 447 insertions(+), 230 deletions(-)