Hi Honnappa,
On 08/11/2021 23:04, Honnappa Nagarahalli wrote:
<snip>
This patch adds a comment for RTE_HASH_BUCKET_ENTRIES explaining why a
particular value was chosen.
Signed-off-by: Vladimir Medvedkin <vladimir.medved...@intel.com>
---
lib/hash/rte_cuckoo_hash.h | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/lib/hash/rte_cuckoo_hash.h b/lib/hash/rte_cuckoo_hash.h index
85be49d3bb..84dc55d86e 100644
--- a/lib/hash/rte_cuckoo_hash.h
+++ b/lib/hash/rte_cuckoo_hash.h
@@ -101,7 +101,13 @@ const rte_hash_cmp_eq_t
cmp_jump_table[NUM_KEY_CMP_CASES] = { #endif
-/** Number of items per bucket. */
+/**
+ * Number of items per bucket.
+ * 8 is a tradeoff between performance and memory consumption.
+ * When it is equal to 8, the sizeof(struct rte_hash_bucket) equal to
+ * RTE_CACHE_LINE_SIZE, thus, there are no gaps in memory between the
+hash
+ * buckets due to their alignment.
+ */
I think this should consider cache lines which are 128B. How about the
following:
"when it is equal to 8, multiple 'struct rte_hash_bucket' can be fit on a single
cache line without any gaps in memory between them".
Sounds good, will add it in v2.
On the other hand, I am wondering if 'struct rte_hash_bucket' needs to have
__rte_cache_aligned attribute. When the memory is allocated for the buckets we
are requesting that it is aligned on the cache line boundary. That should be
sufficient. Removing the attribute will help for local variables. Some
functions (for ex: rte_hash_cuckoo_move_insert_mw) have 2 local variables of
this type and they can be placed on the same cache line if this attribute is
removed.
I see, however I can't find inside the rte_hash_cuckoo_move_insert_mw()
'struct rte_hash_bucket' as local variables, there are only pointers:
struct rte_hash_bucket *cur_bkt;
struct rte_hash_bucket *prev_bkt, *curr_bkt = leaf->bkt;
Yipeng, Sameh, Bruce, what do you think about removing
__rte_cache_aligned attribute?
#define RTE_HASH_BUCKET_ENTRIES 8
#if !RTE_IS_POWER_OF_2(RTE_HASH_BUCKET_ENTRIES)
--
2.25.1
--
Regards,
Vladimir
