Re: [PATCH v6 bpf-next] selftests/bpf: Add benchmark for local_storage get

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Martin KaFai Lau wrote:
> On Tue, Jun 21, 2022 at 12:17:54PM -0700, John Fastabend wrote:
> > > Hashmap Control
> > > ===============
> > >         num keys: 10
> > > hashmap (control) sequential    get:  hits throughput: 20.900 ± 0.334 M ops/s, hits latency: 47.847 ns/op, important_hits throughput: 20.900 ± 0.334 M ops/s
> > > 
> > >         num keys: 1000
> > > hashmap (control) sequential    get:  hits throughput: 13.758 ± 0.219 M ops/s, hits latency: 72.683 ns/op, important_hits throughput: 13.758 ± 0.219 M ops/s
> > > 
> > >         num keys: 10000
> > > hashmap (control) sequential    get:  hits throughput: 6.995 ± 0.034 M ops/s, hits latency: 142.959 ns/op, important_hits throughput: 6.995 ± 0.034 M ops/s
> > > 
> > >         num keys: 100000
> > > hashmap (control) sequential    get:  hits throughput: 4.452 ± 0.371 M ops/s, hits latency: 224.635 ns/op, important_hits throughput: 4.452 ± 0.371 M ops/s
> > > 
> > >         num keys: 4194304
> > > hashmap (control) sequential    get:  hits throughput: 3.043 ± 0.033 M ops/s, hits latency: 328.587 ns/op, important_hits throughput: 3.043 ± 0.033 M ops/s
> > > 
> > 
> > Why is the hashmap lookup not constant with the number of keys? It looks
> > like its prepopulated without collisions so I wouldn't expect any
> > extra ops on the lookup side after looking at the code quickly.
> It may be due to the cpu-cache misses as the map grows.

Maybe but, values are just ints so even 1k * 4B = 4kB should be
inside an otherwise unused server class system. Would be more
believable (to me at least) if the drop off happened at 100k or
more.



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