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

["De Lara Guarch, Pablo" <pablo.de.lara.guarch@intel.com>]

Hi Avinash,

> -----Original Message-----
> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Yeddula, Avinash
> Sent: Monday, October 12, 2015 6:03 PM
> To: Dumitrescu, Cristian; dev@dpdk.org; Bly, Mike
> Subject: Re: [dpdk-dev] DPDK hash function related question
> 
> Hi Cristian,
> I have configured the hash function and it compile fine with "warnings". Since
> librte_hash vs librte_table is 32bit vs 64bit.
> 
> librte_hash library :
> /** Type of function that can be used for calculating the hash value. */
> typedef uint32_t (*rte_hash_function)(const void *key, uint32_t key_len,
> uint32_t init_val);
> 
> librte_table library:
> typedef uint64_t (*rte_table_hash_op_hash) (void *key,	uint32_t
> key_size, uint64_t seed);
> 
> I could use one of these hash functions. This is one option, but our first
> priority is  to use crc hash or cukoo hash.

Mind that cuckoo hash is not a hash function, but a method for resolving collisions in a hash table.

> https://github.com/scylladb/dpdk/blob/master/examples/ip_pipeline/pipeli
> ne/hash_func.h
> 
> We do not want to have those warning in our code. What do you suggest ?
> 
> Thanks
> -Avinash
> 
> -----Original Message-----
> From: Dumitrescu, Cristian [mailto:cristian.dumitrescu@intel.com]
> Sent: Tuesday, September 22, 2015 3:05 AM
> To: Yeddula, Avinash; dev@dpdk.org; Bly, Mike
> Subject: RE: DPDK hash function related question
> 
> 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
> >
>