path: root/tools/testing/selftests/bpf/test_lru_map.c
diff options
authorMartin KaFai Lau <kafai@fb.com>2017-04-14 10:30:29 -0700
committerDavid S. Miller <davem@davemloft.net>2017-04-17 13:55:52 -0400
commit695ba2651a2ecbb336145f9cc033c85b9c6a5cee (patch)
tree8eece29f36fc15ed76516d54eb08368e3d34523f /tools/testing/selftests/bpf/test_lru_map.c
parentbpf: Allow bpf sample programs (*_user.c) to change bpf_map_def (diff)
bpf: lru: Lower the PERCPU_NR_SCANS from 16 to 4
After doing map_perf_test with a much bigger BPF_F_NO_COMMON_LRU map, the perf report shows a lot of time spent in rotating the inactive list (i.e. __bpf_lru_list_rotate_inactive): > map_perf_test 32 8 10000 1000000 | awk '{sum += $3}END{print sum}' 19644783 (19M/s) > map_perf_test 32 8 10000000 10000000 | awk '{sum += $3}END{print sum}' 6283930 (6.28M/s) By inactive, it usually means the element is not in cache. Hence, there is a need to tune the PERCPU_NR_SCANS value. This patch finds a better number of elements to scan during each list rotation. The PERCPU_NR_SCANS (which is defined the same as PERCPU_FREE_TARGET) decreases from 16 elements to 4 elements. This change only affects the BPF_F_NO_COMMON_LRU map. The test_lru_dist does not show meaningful difference between 16 and 4. Our production L4 load balancer which uses the LRU map for conntrack-ing also shows little change in cache hit rate. Since both benchmark and production data show no cache-hit difference, PERCPU_NR_SCANS is lowered from 16 to 4. We can consider making it configurable if we find a usecase later that shows another value works better and/or use a different rotation strategy. After this change: > map_perf_test 32 8 10000000 10000000 | awk '{sum += $3}END{print sum}' 9240324 (9.2M/s) i.e. 6.28M/s -> 9.2M/s The test_lru_dist has not shown meaningful difference: > test_lru_dist zipf.100k.a1_01.out 4000 1: nr_misses: 31575 (Before) vs 31566 (After) > test_lru_dist zipf.100k.a0_01.out 40000 1 nr_misses: 67036 (Before) vs 67031 (After) Signed-off-by: Martin KaFai Lau <kafai@fb.com> Acked-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'tools/testing/selftests/bpf/test_lru_map.c')
1 files changed, 1 insertions, 1 deletions
diff --git a/tools/testing/selftests/bpf/test_lru_map.c b/tools/testing/selftests/bpf/test_lru_map.c
index 87c05e5bdfdd..8c10c9180c1a 100644
--- a/tools/testing/selftests/bpf/test_lru_map.c
+++ b/tools/testing/selftests/bpf/test_lru_map.c
@@ -22,7 +22,7 @@
#include "bpf_util.h"
#define LOCAL_FREE_TARGET (128)
-#define PERCPU_FREE_TARGET (16)
static int nr_cpus;