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

[Yonghong Song]

On 7/21/25 6:01 AM, Matt Fleming wrote:
> On Sat, Jul 19, 2025 at 2:15 PM Jesper Dangaard Brouer <hawk@xxxxxxxxxx> 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.