On 2/5/24 7:00 AM, Marco Elver wrote:
On Wed, 31 Jan 2024 at 20:52, Martin KaFai Lau <martin.lau@xxxxxxxxx> wrote:
[...]
| num_maps: 1000
| local_storage cache sequential get:
| <before> | <after>
| hits throughput: 0.357 ± 0.005 M ops/s | 0.325 ± 0.005 M ops/s (-9.0%)
| hits latency: 2803.738 ns/op | 3076.923 ns/op (+9.7%)
Is it understood why the slow down here? The same goes for the "num_maps: 32"
case above but not as bad as here.
It turned out that there's a real slowdown due to the outlined
slowpath. If I inline everything except for inserting the entry into
the cache (cacheit_lockit codepath is still outlined), the results
look much better even for the case where it always misses the cache.
[...]
diff --git a/tools/testing/selftests/bpf/progs/cgrp_ls_recursion.c b/tools/testing/selftests/bpf/progs/cgrp_ls_recursion.c
index a043d8fefdac..9895087a9235 100644
--- a/tools/testing/selftests/bpf/progs/cgrp_ls_recursion.c
+++ b/tools/testing/selftests/bpf/progs/cgrp_ls_recursion.c
@@ -21,7 +21,7 @@ struct {
__type(value, long);
} map_b SEC(".maps");
-SEC("fentry/bpf_local_storage_lookup")
+SEC("fentry/bpf_local_storage_lookup_slowpath")
The selftest is trying to catch recursion. The change here cannot test the same
thing because the slowpath will never be hit in the test_progs. I don't have a
better idea for now also.
Trying to prepare a v2, and for the test, the only option I see is to
introduce a tracepoint ("bpf_local_storage_lookup"). If unused, should
be a no-op due to static branch.
Or can you suggest different functions to hook to for the recursion test?
I don't prefer to add another tracepoint for the selftest.
The test in "SEC("fentry/bpf_local_storage_lookup")" is testing that the initial
bpf_local_storage_lookup() should work and the immediate recurred
bpf_task_storage_delete() will fail.
Depends on how the new slow path function will look like in v2. The test can
probably be made to go through the slow path, e.g. by creating a lot of task
storage maps before triggering the lookup.
