Zero-copy access to the mempool cache is beneficial for PMD performance, and must be provided by the mempool library to fix [Bug 1052] without a performance regression.
[Bug 1052]: https://bugs.dpdk.org/show_bug.cgi?id=1052 This RFC offers a conceptual zero-copy put function, where the application promises to store some objects, and in return gets an address where to store them. I would like some early feedback. Notes: * Allowing the 'cache' parameter to be NULL, and getting it from the mempool instead, was inspired by rte_mempool_cache_flush(). * Asserting that the 'mp' parameter is not NULL is not done by other functions, so I omitted it here too. NB: Please ignore formatting. Also, this code has not even been compile tested. /** * Promise to put objects in a mempool via zero-copy access to a user-owned mempool cache. * * @param cache * A pointer to the mempool cache. * @param mp * A pointer to the mempool. * @param n * The number of objects to be put in the mempool cache. * @return * The pointer to where to put the objects in the mempool cache. * NULL on error * with rte_errno set appropriately. */ static __rte_always_inline void * rte_mempool_cache_put_bulk_promise(struct rte_mempool_cache *cache, struct rte_mempool *mp, unsigned int n) { void **cache_objs; if (cache == NULL) cache = rte_mempool_default_cache(mp, rte_lcore_id()); if (cache == NULL) { rte_errno = EINVAL; return NULL; } rte_mempool_trace_cache_put_bulk_promise(cache, mp, n); /* The request itself is too big for the cache */ if (unlikely(n > cache->flushthresh)) { rte_errno = EINVAL; return NULL; } /* * The cache follows the following algorithm: * 1. If the objects cannot be added to the cache without crossing * the flush threshold, flush the cache to the backend. * 2. Add the objects to the cache. */ if (cache->len + n <= cache->flushthresh) { cache_objs = &cache->objs[cache->len]; cache->len += n; } else { cache_objs = &cache->objs[0]; rte_mempool_ops_enqueue_bulk(mp, cache_objs, cache->len); cache->len = n; } RTE_MEMPOOL_CACHE_STAT_ADD(cache, put_bulk, 1); RTE_MEMPOOL_CACHE_STAT_ADD(cache, put_objs, n); return cache_objs; } Med venlig hilsen / Kind regards, -Morten Brørup
