Re: [PATCH v3 2/4] hash: reorganize bucket structure

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

> -----Original Message-----
> From: Richardson, Bruce
> Sent: Wednesday, September 28, 2016 2:05 AM
> To: De Lara Guarch, Pablo
> Cc: dev@dpdk.org; Marohn, Byron; Edupuganti, Saikrishna
> Subject: Re: [PATCH v3 2/4] hash: reorganize bucket structure
> 
> On Tue, Sep 06, 2016 at 08:34:02PM +0100, Pablo de Lara wrote:
> > From: Byron Marohn <byron.marohn@intel.com>
> >
> > Move current signatures of all entries together in the bucket
> > and same with all alternative signatures, instead of having
> > current and alternative signatures together per entry in the bucket.
> > This will be benefitial in the next commits, where a vectorized
> > comparison will be performed, achieving better performance.
> >
> > Signed-off-by: Byron Marohn <byron.marohn@intel.com>
> > Signed-off-by: Saikrishna Edupuganti <saikrishna.edupuganti@intel.com>
> > ---
> >  lib/librte_hash/rte_cuckoo_hash.c     | 43 ++++++++++++++++++----------------
> -
> >  lib/librte_hash/rte_cuckoo_hash.h     | 17 ++++----------
> >  lib/librte_hash/rte_cuckoo_hash_x86.h | 20 ++++++++--------
> >  3 files changed, 37 insertions(+), 43 deletions(-)
> >
> <snip>
> > --- a/lib/librte_hash/rte_cuckoo_hash.h
> > +++ b/lib/librte_hash/rte_cuckoo_hash.h
> > @@ -151,17 +151,6 @@ struct lcore_cache {
> >  	void *objs[LCORE_CACHE_SIZE]; /**< Cache objects */
> >  } __rte_cache_aligned;
> >
> > -/* Structure storing both primary and secondary hashes */
> > -struct rte_hash_signatures {
> > -	union {
> > -		struct {
> > -			hash_sig_t current;
> > -			hash_sig_t alt;
> > -		};
> > -		uint64_t sig;
> > -	};
> > -};
> > -
> >  /* Structure that stores key-value pair */
> >  struct rte_hash_key {
> >  	union {
> > @@ -174,10 +163,14 @@ struct rte_hash_key {
> >
> >  /** Bucket structure */
> >  struct rte_hash_bucket {
> > -	struct rte_hash_signatures signatures[RTE_HASH_BUCKET_ENTRIES];
> > +	hash_sig_t sig_current[RTE_HASH_BUCKET_ENTRIES];
> > +
> >  	/* Includes dummy key index that always contains index 0 */
> >  	uint32_t key_idx[RTE_HASH_BUCKET_ENTRIES + 1];
> > +
> >  	uint8_t flag[RTE_HASH_BUCKET_ENTRIES];
> > +
> > +	hash_sig_t sig_alt[RTE_HASH_BUCKET_ENTRIES];
> >  } __rte_cache_aligned;
> >
> 
> Is there a reason why sig_current and sig_alt fields cannot be beside each
> other in the structure. It looks strange having them separate by other fields?

Bucket entries has increased to 8 now, so sig_current and key_idx take 64 bytes
(key_idx will be reduced to 8 entries in the fourth patch).

Therefore, the idea was to push sig_alt to the next cache line
(assuming a 64 byte cacheline, if it is bigger, then either way is ok),
as it is not used in lookup (like sig_current and key_idx).

Anyway, I think I will move sig_alt before flag, so it is cache aligned,
in case vectorization is used in the future.

Thanks,
Pablo

> 
> /Bruce