[PATCH v2 0/1] mempool: implement index-based per core cache

[Dharmik Thakkar <dharmik.thakkar@arm.com>]

Current mempool per core cache implementation stores pointers to mbufs
On 64b architectures, each pointer consumes 8B
This patch replaces it with index-based implementation,
where in each buffer is addressed by (pool base address + index)
It reduces the amount of memory/cache required for per core cache

L3Fwd performance testing reveals minor improvements in the cache
performance (L1 and L2 misses reduced by 0.60%)
with no change in throughput

Micro-benchmarking the patch using mempool_perf_test shows
significant improvement with majority of the test cases

Number of cores = 1:
n_get_bulk=1 n_put_bulk=1 n_keep=32 %_change_with_patch=18.01
n_get_bulk=1 n_put_bulk=1 n_keep=128 %_change_with_patch=19.91
n_get_bulk=1 n_put_bulk=4 n_keep=32 %_change_with_patch=-20.37 (regression)
n_get_bulk=1 n_put_bulk=4 n_keep=128 %_change_with_patch=-17.01 (regression) 
n_get_bulk=1 n_put_bulk=32 n_keep=32 %_change_with_patch=-25.06 (regression)
n_get_bulk=1 n_put_bulk=32 n_keep=128 %_change_with_patch=-23.81 (regression)
n_get_bulk=4 n_put_bulk=1 n_keep=32 %_change_with_patch=53.93
n_get_bulk=4 n_put_bulk=1 n_keep=128 %_change_with_patch=60.90
n_get_bulk=4 n_put_bulk=4 n_keep=32 %_change_with_patch=1.64
n_get_bulk=4 n_put_bulk=4 n_keep=128 %_change_with_patch=8.76
n_get_bulk=4 n_put_bulk=32 n_keep=32 %_change_with_patch=-4.71 (regression)
n_get_bulk=4 n_put_bulk=32 n_keep=128 %_change_with_patch=-3.19 (regression)
n_get_bulk=32 n_put_bulk=1 n_keep=32 %_change_with_patch=65.63
n_get_bulk=32 n_put_bulk=1 n_keep=128 %_change_with_patch=75.19
n_get_bulk=32 n_put_bulk=4 n_keep=32 %_change_with_patch=11.75
n_get_bulk=32 n_put_bulk=4 n_keep=128 %_change_with_patch=15.52
n_get_bulk=32 n_put_bulk=32 n_keep=32 %_change_with_patch=13.45
n_get_bulk=32 n_put_bulk=32 n_keep=128 %_change_with_patch=11.58

Number of core = 2:
n_get_bulk=1 n_put_bulk=1 n_keep=32 %_change_with_patch=18.21
n_get_bulk=1 n_put_bulk=1 n_keep=128 %_change_with_patch=21.89
n_get_bulk=1 n_put_bulk=4 n_keep=32 %_change_with_patch=-21.21 (regression)
n_get_bulk=1 n_put_bulk=4 n_keep=128 %_change_with_patch=-17.05 (regression)
n_get_bulk=1 n_put_bulk=32 n_keep=32 %_change_with_patch=-26.09 (regression)
n_get_bulk=1 n_put_bulk=32 n_keep=128 %_change_with_patch=-23.49 (regression)
n_get_bulk=4 n_put_bulk=1 n_keep=32 %_change_with_patch=56.28
n_get_bulk=4 n_put_bulk=1 n_keep=128 %_change_with_patch=67.69
n_get_bulk=4 n_put_bulk=4 n_keep=32 %_change_with_patch=1.45
n_get_bulk=4 n_put_bulk=4 n_keep=128 %_change_with_patch=8.84
n_get_bulk=4 n_put_bulk=32 n_keep=32 %_change_with_patch=-5.27 (regression)
n_get_bulk=4 n_put_bulk=32 n_keep=128 %_change_with_patch=-3.09 (regression)
n_get_bulk=32 n_put_bulk=1 n_keep=32 %_change_with_patch=76.11
n_get_bulk=32 n_put_bulk=1 n_keep=128 %_change_with_patch=86.06
n_get_bulk=32 n_put_bulk=4 n_keep=32 %_change_with_patch=11.86
n_get_bulk=32 n_put_bulk=4 n_keep=128 %_change_with_patch=16.55
n_get_bulk=32 n_put_bulk=32 n_keep=32 %_change_with_patch=13.01
n_get_bulk=32 n_put_bulk=32 n_keep=128 %_change_with_patch=11.51


From analyzing the results, it is clear that for n_get_bulk and
n_put_bulk sizes of 32 there is no performance regression
IMO, the other sizes are not practical from performance perspective
and the regression in those cases can be safely ignored

An attempt to increase the size of mempool to 32GB, by dividing the
index by sizeof(uintptr_t), has led to a performance degradation of
~5% compared to the base performance
---
v2:
 - Increase size of mempool to 32GB (Morten)
 - Improve performance for other platforms using dual loop unrolling
---
Dharmik Thakkar (1):
  mempool: implement index-based per core cache

 lib/mempool/rte_mempool.h             | 150 +++++++++++++++++++++++++-
 lib/mempool/rte_mempool_ops_default.c |   7 ++
 2 files changed, 156 insertions(+), 1 deletion(-)

-- 
2.17.1