> -----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>
