Re: [dpdk-dev] DPDK hash function related question

["Dumitrescu, Cristian" <cristian.dumitrescu@intel.com>]

Hi Avinash,

Yes, the hash function is configurable.

Are you using a DPDK release older than 2.1? In DPDK we moved away from test_hash to CRC-based hashes. Please take a look at DPDK release 2.1 examples/ip_pipeline application: in pipeline_flow_classification_be.c, we use CRC-based hash functions defined in file hash_func.h from the same folder.

Regards,
Cristian

> -----Original Message-----
> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Yeddula, Avinash
> Sent: Tuesday, September 22, 2015 1:34 AM
> To: dev@dpdk.org; Bly, Mike
> Subject: [dpdk-dev] DPDK hash function related question
> 
> Hello All,
> 
> I'm DPDK extensible bucket hash in the rte_table library of packet
> framework. My question is related to the actual hash function that computes
> the hash signature.
> 
> All the available examples have initialized it to test_hash.   I do not see any
> hash function available in rte_table library , that computes the actual
> signature
> 
> 
> 
> struct rte_table_hash_ext_params   hash_table_params = {
> 
>     .key_size = TABLE_ENTRY_KEY_SIZE,
> 
>     .n_keys = TABLE_MAX_SIZE,
> 
>     .n_buckets = TABLE_MAX_BUCKET_COUNT,
> 
>     .n_buckets_ext = TABLE_MAX_EXT_BUCKET_COUNT,
> 
>     .f_hash = test_hash,
> 
>     .seed = 0,
> 
>     .signature_offset = 0;
> 
>     .key_offset = __builtin_offsetof(struct metadata_t, tbl_key),
> 
> };
> 
> 
> 
> So, I wanted to use hash functions from DPDK rte_hash library. This is what
> I'm doing and looking at the code this looks ok to me.
> 
> I'm at least a week or 2 away from testing this part of the code. I wanted to
> confirm that, there is no fundamental flaw in using the DPDK rte_hash library
> and rte_table library like this. Could someone confirm this please ?
> 
> 
> 
> #define DEFAULT_HASH_FUNC rte_hash_crc
> 
> 
> 
> struct rte_table_hash_ext_params   hash_table_params = {
> 
>     .key_size = TABLE_ENTRY_KEY_SIZE,
> 
>     .n_keys = TABLE_MAX_SIZE,
> 
>     .n_buckets = TABLE_MAX_BUCKET_COUNT,
> 
>     .n_buckets_ext = TABLE_MAX_EXT_BUCKET_COUNT,
> 
>     .f_hash = DEFAULT_HASH_FUNC ,
> 
>     .seed = 0,
> 
>     .signature_offset = 0;
> 
>     .key_offset = __builtin_offsetof(struct metadata_t, tbl_key),
> 
> };
> 
> 
> 
> Thanks
> 
> -Avinash
>