Re: [PATCH] selftests/bpf: Add LPM trie microbenchmarks

[Yonghong Song <yonghong.song@linux.dev>]

On 7/21/25 6:01 AM, Matt Fleming wrote:
> On Sat, Jul 19, 2025 at 2:15 PM Jesper Dangaard Brouer <hawk@kernel.org> wrote:
>> On 18/07/2025 17.05, Matt Fleming wrote:
>>
>>> [...]
>>> diff --git a/tools/testing/selftests/bpf/progs/lpm_trie_bench.c b/tools/testing/selftests/bpf/progs/lpm_trie_bench.c
>>> new file mode 100644
>>> index 000000000000..c335718cc240
>>> --- /dev/null
>>> +++ b/tools/testing/selftests/bpf/progs/lpm_trie_bench.c
>>> @@ -0,0 +1,175 @@
>> [...]
>>> +
>>> +static __always_inline void atomic_inc(long *cnt)
>>> +{
>>> +     __atomic_add_fetch(cnt, 1, __ATOMIC_SEQ_CST);
>>> +}
>>> +
>>> +static __always_inline long atomic_swap(long *cnt, long val)
>>> +{
>>> +     return __atomic_exchange_n(cnt, val, __ATOMIC_SEQ_CST);
>>> +}
>> For userspace includes we have similar defines in bench.h.
>> Except they use __ATOMIC_RELAXED and here __ATOMIC_SEQ_CST.
>> Which is the correct to use?
>>
>> For BPF kernel-side do selftests have another header file that define
>> these `atomic_inc` and `atomic_swap` ?
> Actually, we can side step this problem completely by consistently
> using __sync_fetch_and_add() for duration_ns and hits and removing the
> atomic operations for DELETE, which doesn't need atomicity anyway
> since only a single producer can run.

__sync_fetch_and_add() and __atomic_add_fetch() have the same
semantics. So indeed tt would be good to just use one of them.

>
> I'll send a v2.