[PATCH v4 0/2] Optimize performance of update hash-map when free is zero
From: Feng zhou
Date: Wed Jun 01 2022 - 04:42:11 EST
From: Feng Zhou <zhoufeng.zf@xxxxxxxxxxxxx>
We encountered bad case on big system with 96 CPUs that
alloc_htab_elem() would last for 1ms. The reason is that after the
prealloc hashtab has no free elems, when trying to update, it will still
grab spin_locks of all cpus. If there are multiple update users, the
competition is very serious.
0001: Add is_empty to check whether the free list is empty or not before taking
the lock.
0002: Add benchmark to reproduce this worst case.
Changelog:
v3->v4: Addressed comments from Daniel Borkmann.
- Use READ_ONCE/WRITE_ONCE.
some details in here:
https://lore.kernel.org/all/20220530091340.53443-1-zhoufeng.zf@xxxxxxxxxxxxx/
v2->v3: Addressed comments from Alexei Starovoitov, Andrii Nakryiko.
- Adjust the way the benchmark is tested.
- Adjust the code format.
some details in here:
https://lore.kernel.org/all/20220524075306.32306-1-zhoufeng.zf@xxxxxxxxxxxxx/T/
v1->v2: Addressed comments from Alexei Starovoitov.
- add a benchmark to reproduce the issue.
- Adjust the code format that avoid adding indent.
some details in here:
https://lore.kernel.org/all/877ac441-045b-1844-6938-fcaee5eee7f2@xxxxxxxxxxxxx/T/
Feng Zhou (2):
bpf: avoid grabbing spin_locks of all cpus when no free elems
selftest/bpf/benchs: Add bpf_map benchmark
kernel/bpf/percpu_freelist.c | 28 +++++-
kernel/bpf/percpu_freelist.h | 1 +
tools/testing/selftests/bpf/Makefile | 4 +-
tools/testing/selftests/bpf/bench.c | 2 +
.../benchs/bench_bpf_hashmap_full_update.c | 96 +++++++++++++++++++
.../run_bench_bpf_hashmap_full_update.sh | 11 +++
.../bpf/progs/bpf_hashmap_full_update_bench.c | 40 ++++++++
7 files changed, 178 insertions(+), 4 deletions(-)
create mode 100644 tools/testing/selftests/bpf/benchs/bench_bpf_hashmap_full_update.c
create mode 100755 tools/testing/selftests/bpf/benchs/run_bench_bpf_hashmap_full_update.sh
create mode 100644 tools/testing/selftests/bpf/progs/bpf_hashmap_full_update_bench.c
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2.20.1