netdev - [PATCH v2 0/2] Optimize performance of update hash-map when free is zero

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Date:   Tue, 24 May 2022 15:53:04 +0800
From:   Feng zhou <zhoufeng.zf@...edance.com>
To:     ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
        kafai@...com, songliubraving@...com, yhs@...com,
        john.fastabend@...il.com, kpsingh@...nel.org
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org, duanxiongchun@...edance.com,
        songmuchun@...edance.com, wangdongdong.6@...edance.com,
        cong.wang@...edance.com, zhouchengming@...edance.com,
        zhoufeng.zf@...edance.com
Subject: [PATCH v2 0/2] Optimize performance of update hash-map when free is zero

From: Feng Zhou <zhoufeng.zf@...edance.com>

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:
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@bytedance.com/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 +
 .../selftests/bpf/benchs/bench_bpf_map.c      | 78 +++++++++++++++++++
 .../selftests/bpf/benchs/run_bench_bpf_map.sh | 10 +++
 .../selftests/bpf/progs/bpf_map_bench.c       | 27 +++++++
 7 files changed, 146 insertions(+), 4 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/benchs/bench_bpf_map.c
 create mode 100755 tools/testing/selftests/bpf/benchs/run_bench_bpf_map.sh
 create mode 100644 tools/testing/selftests/bpf/progs/bpf_map_bench.c

-- 
2.20.1