[dpdk-dev] [PATCH 3/3] lib/hash: adjust tbl_chng_cnt position
Wang, Yipeng1
yipeng1.wang at intel.com
Fri Jun 28 20:50:16 CEST 2019
>-----Original Message-----
>From: Honnappa Nagarahalli [mailto:honnappa.nagarahalli at arm.com]
>Sent: Tuesday, June 25, 2019 2:15 PM
>To: Wang, Yipeng1 <yipeng1.wang at intel.com>; Gobriel, Sameh <sameh.gobriel at intel.com>; Richardson, Bruce
><bruce.richardson at intel.com>; De Lara Guarch, Pablo <pablo.de.lara.guarch at intel.com>; honnappa.nagarahalli at arm.com
>Cc: gavin.hu at arm.com; ruifeng.wang at arm.com; dev at dpdk.org; nd at arm.com; stable at dpdk.org
>Subject: [PATCH 3/3] lib/hash: adjust tbl_chng_cnt position
>
>tbl_chng_cnt is one of the first elements of the structure used in
>the lookup. Move it to the beginning of the cache line to gain
>performance.
>
>Fixes: e605a1d36 ("hash: add lock-free r/w concurrency")
>Cc: stable at dpdk.org
>
>Signed-off-by: Honnappa Nagarahalli <honnappa.nagarahalli at arm.com>
>Reviewed-by: Gavin Hu <gavin.hu at arm.com>
>Tested-by: Ruifeng Wang <ruifeng.wang at arm.com>
>---
> lib/librte_hash/rte_cuckoo_hash.h | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
>diff --git a/lib/librte_hash/rte_cuckoo_hash.h b/lib/librte_hash/rte_cuckoo_hash.h
>index fb19bb27d..af6451b5c 100644
>--- a/lib/librte_hash/rte_cuckoo_hash.h
>+++ b/lib/librte_hash/rte_cuckoo_hash.h
>@@ -170,7 +170,9 @@ struct rte_hash {
>
> /* Fields used in lookup */
>
>- uint32_t key_len __rte_cache_aligned;
>+ uint32_t *tbl_chng_cnt __rte_cache_aligned;
>+ /**< Indicates if the hash table changed from last read. */
>+ uint32_t key_len;
> /**< Length of hash key. */
> uint8_t hw_trans_mem_support;
> /**< If hardware transactional memory is used. */
>@@ -218,8 +220,6 @@ struct rte_hash {
> * is piggy-backed to freeing of the key index.
> */
> uint32_t *ext_bkt_to_free;
>- uint32_t *tbl_chng_cnt;
>- /**< Indicates if the hash table changed from last read. */
> } __rte_cache_aligned;
>
> struct queue_node {
>--
>2.17.1
[Wang, Yipeng]
I am not sure about this change. By moving counter to front, I think you seems push key_store out of the cache line. And key_store
Is also used in lookup (and more commonly).
My tests also show perf drop in many cases.
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