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authorEduard Zingerman <eddyz87@gmail.com>2023-11-21 05:06:53 +0300
committerAlexei Starovoitov <ast@kernel.org>2023-11-21 05:33:35 +0300
commitf40bfd1679446b22d321e64a1fa98b7d07d2be08 (patch)
treeb945d735226e100b89d9b9e39e5c0fa0f010d1ba /tools
parent87eb0152bcc102ecbda866978f4e54db5a3be1ef (diff)
downloadlinux-f40bfd1679446b22d321e64a1fa98b7d07d2be08.tar.xz
selftests/bpf: fix bpf_loop_bench for new callback verification scheme
This is a preparatory change. A follow-up patch "bpf: verify callbacks as if they are called unknown number of times" changes logic for callbacks handling. While previously callbacks were verified as a single function call, new scheme takes into account that callbacks could be executed unknown number of times. This has dire implications for bpf_loop_bench: SEC("fentry/" SYS_PREFIX "sys_getpgid") int benchmark(void *ctx) { for (int i = 0; i < 1000; i++) { bpf_loop(nr_loops, empty_callback, NULL, 0); __sync_add_and_fetch(&hits, nr_loops); } return 0; } W/o callbacks change verifier sees it as a 1000 calls to empty_callback(). However, with callbacks change things become exponential: - i=0: state exploring empty_callback is scheduled with i=0 (a); - i=1: state exploring empty_callback is scheduled with i=1; ... - i=999: state exploring empty_callback is scheduled with i=999; - state (a) is popped from stack; - i=1: state exploring empty_callback is scheduled with i=1; ... Avoid this issue by rewriting outer loop as bpf_loop(). Unfortunately, this adds a function call to a loop at runtime, which negatively affects performance: throughput latency before: 149.919 ± 0.168 M ops/s, 6.670 ns/op after : 137.040 ± 0.187 M ops/s, 7.297 ns/op Acked-by: Andrii Nakryiko <andrii@kernel.org> Signed-off-by: Eduard Zingerman <eddyz87@gmail.com> Link: https://lore.kernel.org/r/20231121020701.26440-4-eddyz87@gmail.com Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'tools')
-rw-r--r--tools/testing/selftests/bpf/progs/bpf_loop_bench.c13
1 files changed, 8 insertions, 5 deletions
diff --git a/tools/testing/selftests/bpf/progs/bpf_loop_bench.c b/tools/testing/selftests/bpf/progs/bpf_loop_bench.c
index 4ce76eb064c4..d461746fd3c1 100644
--- a/tools/testing/selftests/bpf/progs/bpf_loop_bench.c
+++ b/tools/testing/selftests/bpf/progs/bpf_loop_bench.c
@@ -15,13 +15,16 @@ static int empty_callback(__u32 index, void *data)
return 0;
}
+static int outer_loop(__u32 index, void *data)
+{
+ bpf_loop(nr_loops, empty_callback, NULL, 0);
+ __sync_add_and_fetch(&hits, nr_loops);
+ return 0;
+}
+
SEC("fentry/" SYS_PREFIX "sys_getpgid")
int benchmark(void *ctx)
{
- for (int i = 0; i < 1000; i++) {
- bpf_loop(nr_loops, empty_callback, NULL, 0);
-
- __sync_add_and_fetch(&hits, nr_loops);
- }
+ bpf_loop(1000, outer_loop, NULL, 0);
return 0;
}