netdev - RE: [PATCH bpf-next] selftests/bpf: Add BPF trampoline performance test

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Date:   Fri, 22 Nov 2019 09:37:12 -0800
From:   John Fastabend <john.fastabend@...il.com>
To:     Alexei Starovoitov <ast@...nel.org>, davem@...emloft.net
Cc:     daniel@...earbox.net, netdev@...r.kernel.org, bpf@...r.kernel.org,
        kernel-team@...com
Subject: RE: [PATCH bpf-next] selftests/bpf: Add BPF trampoline performance
 test

Alexei Starovoitov wrote:
> Add a test that benchmarks different ways of attaching BPF program to a kernel function.
> Here are the results for 2.4Ghz x86 cpu on a kernel without mitigations:
> $ ./test_progs -n 49 -v|grep events
> task_rename base	2743K events per sec
> task_rename kprobe	2419K events per sec
> task_rename kretprobe	1876K events per sec
> task_rename raw_tp	2578K events per sec
> task_rename fentry	2710K events per sec
> task_rename fexit	2685K events per sec
> 
> On a kernel with retpoline:
> $ ./test_progs -n 49 -v|grep events
> task_rename base	2401K events per sec
> task_rename kprobe	1930K events per sec
> task_rename kretprobe	1485K events per sec
> task_rename raw_tp	2053K events per sec
> task_rename fentry	2351K events per sec
> task_rename fexit	2185K events per sec
> 
> All 5 approaches:
> - kprobe/kretprobe in __set_task_comm()
> - raw tracepoint in trace_task_rename()
> - fentry/fexit in __set_task_comm()
> are roughly equivalent.
> 
> __set_task_comm() by itself is quite fast, so any extra instructions add up.
> Until BPF trampoline was introduced the fastest mechanism was raw tracepoint.
> kprobe via ftrace was second best. kretprobe is slow due to trap. New
> fentry/fexit methods via BPF trampoline are clearly the fastest and the
> difference is more pronounced with retpoline on, since BPF trampoline doesn't
> use indirect jumps.
> 
> Signed-off-by: Alexei Starovoitov <ast@...nel.org>
> ---
>  .../selftests/bpf/prog_tests/test_overhead.c  | 142 ++++++++++++++++++
>  .../selftests/bpf/progs/test_overhead.c       |  43 ++++++
>  2 files changed, 185 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/test_overhead.c
>  create mode 100644 tools/testing/selftests/bpf/progs/test_overhead.c
> 
> diff --git a/tools/testing/selftests/bpf/prog_tests/test_overhead.c b/tools/testing/selftests/bpf/prog_tests/test_overhead.c
> new file mode 100644
> index 000000000000..c32aa28bd93f

Acked-by: John Fastabend <john.fastabend@...il.com>