On Tue, Jun 21, 2022 at 10:49:46PM -0700, John Fastabend wrote: > 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. It is not only value (and key) size. There is overhead. htab_elem alone is 48bytes. key and value need to 8bytes align also. >From a random machine: lscpu -C NAME ONE-SIZE ALL-SIZE WAYS TYPE LEVEL SETS PHY-LINE COHERENCY-SIZE L1d 32K 576K 8 Data 1 64 1 64 L1i 32K 576K 8 Instruction 1 64 1 64 L2 1M 18M 16 Unified 2 1024 1 64 L3 24.8M 24.8M 11 Unified 3 36864 1 64
