[dpdk-dev] [PATCH v4 0/4] Cuckoo hash enhancements

[Gobriel, Sameh]

> -----Original Message-----
> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of De Lara Guarch, Pablo
> Sent: Friday, September 30, 2016 12:39 AM
> To: dev at dpdk.org
> Cc: Richardson, Bruce <bruce.richardson at intel.com>; De Lara Guarch, Pablo
> <pablo.de.lara.guarch at intel.com>
> Subject: [dpdk-dev] [PATCH v4 0/4] Cuckoo hash enhancements
> 
> This patchset improves lookup performance on the current hash library by
> changing the existing lookup bulk pipeline, with an improved pipeline, based on
> a loop-and-jump model, instead of the current 4-stage 2-entry pipeline.
> Also, x86 vectorized intrinsics are used to improve performance when
> comparing signatures.
> 
> First patch reorganizes the order of the hash structure.
> The structure takes more than one 64-byte cache line, but not all the fields are
> used in the lookup operation (the most common operation).
> Therefore, all these fields have been moved to the first part of the structure, so
> they all fit in one cache line, improving slightly the performance in some
> scenarios.
> 
> Second patch modifies the order of the bucket structure.
> Currently, the buckets store all the signatures together (current and
> alternative).
> In order to be able to perform a vectorized signature comparison, all current
> signatures have to be together, so the order of the bucket has been changed,
> having separated all the current signatures from the alternative signatures.
> 
> Third patch introduces x86 vectorized intrinsics.
> When performing a lookup bulk operation, all current signatures in a bucket
> are compared against the signature of the key being looked up.
> Now that they all are together, a vectorized comparison can be performed,
> which takes less instructions to be carried out.
> In case of having a machine with AVX2, number of entries per bucket are
> increased from 4 to 8, as AVX2 allows comparing two 256-bit values, with
> 8x32-bit integers, which are the 8 signatures on the bucket.
> 
> Fourth (and last) patch modifies the current pipeline of the lookup bulk
> function.
> The new pipeline is based on a loop-and-jump model. The two key
> improvements are:
> 
> - Better prefetching: in this case, first 4 keys to be looked up are prefetched,
>   and after that, the rest of the keys are prefetched at the time the calculation
>   of the signatures are being performed. This gives more time for the CPU to
>   prefetch the data requesting before actually need it, which result in less
>   cache misses and therefore, higher throughput.
> 
> - Lower performance penalty when using fallback: the lookup bulk algorithm
>   assumes that most times there will not be a collision in a bucket, but it might
>   happen that two or more signatures are equal, which means that more than
> one
>   key comparison might be necessary. In that case, only the key of the first hit is
> prefetched,
>   like in the current implementation. The difference now is that if this
> comparison
>   results in a miss, the information of the other keys to be compared has been
> stored,
>   unlike the current implementation, which needs to perform an entire simple
> lookup again.
> 
> Changes in v4:
> - Reordered hash structure, so alt signature is at the start
>   of the next cache line, and explain in the commit message
>   why it has been moved
> - Reordered hash structure, so name field is on top of the structure,
>   leaving all the fields used in lookup in the next cache line
>   (instead of the first cache line)
> 
> Changes in v3:
> - Corrected the cover letter (wrong number of patches)
> 
> Changes in v2:
> - Increased entries per bucket from 4 to 8 for all cases,
>   so it is not architecture dependent any longer.
> - Replaced compile-time signature comparison function election
>   with run-time election, so best optimization available
>   will be used from a single binary.
> - Reordered the hash structure, so all the fields used by lookup
>   are in the same cache line (first).
> 
> Byron Marohn (3):
>   hash: reorganize bucket structure
>   hash: add vectorized comparison
>   hash: modify lookup bulk pipeline
> 
> Pablo de Lara (1):
>   hash: reorder hash structure
> 
>  lib/librte_hash/rte_cuckoo_hash.c     | 455 ++++++++++++++--------------------
>  lib/librte_hash/rte_cuckoo_hash.h     |  56 +++--
>  lib/librte_hash/rte_cuckoo_hash_x86.h |  20 +-
>  3 files changed, 228 insertions(+), 303 deletions(-)
> 
> --
> 2.7.4

Series-acked-by: Sameh Gobriel <sameh.gobriel at intel.com>