Re: [PATCH v3 1/2] librte_lpm: Improve performance of the delete and add functions

[Alex Kiselev <alex@therouter.net>]

> On Wed, 11 Jul 2018 20:53:46 +0300
> Alex Kiselev <alex@therouter.net> wrote:

>> librte_lpm: Improve lpm6 performance

...

>>  
>>       /* LPM Tables. */
>> -     struct rte_lpm6_rule *rules_tbl; /**< LPM rules. */
>> +     struct rte_mempool *rules_pool; /**< LPM rules mempool. */
>> +     struct rte_hash *rules_tbl; /**< LPM rules. */
>>       struct rte_lpm6_tbl_entry tbl24[RTE_LPM6_TBL24_NUM_ENTRIES]
>>                       __rte_cache_aligned; /**< LPM tbl24 table. */
>>       struct rte_lpm6_tbl_entry tbl8[0]
>> @@ -93,22 +106,81 @@ struct rte_lpm6 {
>>   * and set the rest to 0.


> What is the increased memory overhead of having a hash table?
compared to the current rules array it's about 2 times since a prefix is stored in
a rule (mempool) and in a rule key (hashtable). 
I am only talking here about the rule storage.

And I've just realised it doesn't have to be this
way, I don't need the rules mempool anymore. I only need the rules hashtable, since 
it could contains everything a rule needs. A rule prefix is stored in a hash key, 
and a next hop index could be stored in a hash value. That would eliminate memory overhead.

I'll try this way in next patch series.

> Wouldn't it make more sense to use something like tree, and use left/right
> in the rules entry. That way the memory is spread and scales with the number
> of rules.
Maybe. But there is no tree library in the DPDK. So I choose 
a fast and simple way to implement
rules storage using the existent hashtable lib.
And it gives good perfomance results.

Anyway, it's not a data plane, add/delete operations are 
executed not very often, so it's not critical to find
the most efficient (in terms of memory consumption) way, a good one is ok.

> Remember on a internet router, it is not unusual to 2M or more rules.

> Also. Please run checkpatch shell script on your patches.  For example, there
> should be blank line between declarations and code.
I have. It didn't give me any warnings.




-- 
Alex