On 12/24/22 14:55, Morten Brørup wrote:
Zero-copy access to mempool caches 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
Bugzilla ID: 1052
v4:
* Fix checkpatch warnings.
v3:
* Bugfix: Respect the cache size; compare to the flush threshold instead
of RTE_MEMPOOL_CACHE_MAX_SIZE.
* Added 'rewind' function for incomplete 'put' operations. (Konstantin)
* Replace RTE_ASSERTs with runtime checks of the request size.
Instead of failing, return NULL if the request is too big. (Konstantin)
* Modified comparison to prevent overflow if n is really huge and len is
non-zero.
* Updated the comments in the code.
v2:
* Fix checkpatch warnings.
* Fix missing registration of trace points.
* The functions are inline, so they don't go into the map file.
v1 changes from the RFC:
* Removed run-time parameter checks. (Honnappa)
This is a hot fast path function; requiring correct application
behaviour, i.e. function parameters must be valid.
* Added RTE_ASSERT for parameters instead.
Code for this is only generated if built with RTE_ENABLE_ASSERT.
* Removed fallback when 'cache' parameter is not set. (Honnappa)
* Chose the simple get function; i.e. do not move the existing objects in
the cache to the top of the new stack, just leave them at the bottom.
* Renamed the functions. Other suggestions are welcome, of course. ;-)
* Updated the function descriptions.
* Added the functions to trace_fp and version.map.
Signed-off-by: Morten Brørup <m...@smartsharesystems.com>
[snip]
diff --git a/lib/mempool/rte_mempool.h b/lib/mempool/rte_mempool.h
index 9f530db24b..00387e7543 100644
--- a/lib/mempool/rte_mempool.h
+++ b/lib/mempool/rte_mempool.h
[snip]
@@ -1346,6 +1347,170 @@ rte_mempool_cache_flush(struct rte_mempool_cache *cache,
cache->len = 0;
}
+/**
+ * @warning
+ * @b EXPERIMENTAL: This API may change, or be removed, without prior notice.
+ *
+ * Zero-copy put objects in a user-owned mempool cache backed by the specified
mempool.
+ *
+ * @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 if the request itself is too big for the cache, i.e.
+ * exceeds the cache flush threshold.
+ */
+__rte_experimental
+static __rte_always_inline void *
+rte_mempool_cache_zc_put_bulk(struct rte_mempool_cache *cache,
+ struct rte_mempool *mp,
+ unsigned int n)
+{
+ void **cache_objs;
+
+ RTE_ASSERT(cache != NULL);
+ RTE_ASSERT(mp != NULL);
+
+ rte_mempool_trace_cache_zc_put_bulk(cache, mp, n);
Wouldn't it be better to do tracing nearby return value to
trace return value as well?
+
+ if (n <= cache->flushthresh - cache->len) {
+ /*
+ * The objects can be added to the cache without crossing the
+ * flush threshold.
+ */
+ cache_objs = &cache->objs[cache->len];
+ cache->len += n;
+ } else if (likely(n <= cache->flushthresh)) {
+ /*
+ * The request itself fits into the cache.
+ * But first, the cache must be flushed to the backend, so
+ * adding the objects does not cross the flush threshold.
+ */
+ cache_objs = &cache->objs[0];
+ rte_mempool_ops_enqueue_bulk(mp, cache_objs, cache->len);
+ cache->len = n;
+ } else {
+ /* The request itself is too big for the cache. */
+ return NULL;
+ }
+
+ RTE_MEMPOOL_CACHE_STAT_ADD(cache, put_bulk, 1);
+ RTE_MEMPOOL_CACHE_STAT_ADD(cache, put_objs, n);
It duplicates put function code. Shouldn't put function use
this one to avoid duplication?
+
+ return cache_objs;
+}
+
+/**
+ * @warning
+ * @b EXPERIMENTAL: This API may change, or be removed, without prior notice.
+ *
+ * Zero-copy un-put objects in a user-owned mempool cache.
+ *
+ * @param cache
+ * A pointer to the mempool cache.
+ * @param n
+ * The number of objects not put in the mempool cache after calling
+ * rte_mempool_cache_zc_put_bulk().
+ */
+__rte_experimental
+static __rte_always_inline void
+rte_mempool_cache_zc_put_rewind(struct rte_mempool_cache *cache,
+ unsigned int n)
+{
+ RTE_ASSERT(cache != NULL);
+ RTE_ASSERT(n <= cache->len);
+
+ rte_mempool_trace_cache_zc_put_rewind(cache, n);
+
+ cache->len -= n;
+
+ RTE_MEMPOOL_CACHE_STAT_ADD(cache, put_objs, (int)-n);
+}
+
+/**
+ * @warning
+ * @b EXPERIMENTAL: This API may change, or be removed, without prior notice.
+ *
+ * Zero-copy get objects from a user-owned mempool cache backed by the
specified mempool.
+ *
+ * @param cache
+ * A pointer to the mempool cache.
+ * @param mp
+ * A pointer to the mempool.
+ * @param n
+ * The number of objects to prefetch into the mempool cache.
+ * @return
+ * The pointer to the objects in the mempool cache.
+ * NULL on error; i.e. the cache + the pool does not contain 'n' objects.
+ * With rte_errno set to the error code of the mempool dequeue function,
+ * or EINVAL if the request itself is too big for the cache, i.e.
+ * exceeds the cache flush threshold.
+ */
+__rte_experimental
+static __rte_always_inline void *
+rte_mempool_cache_zc_get_bulk(struct rte_mempool_cache *cache,
+ struct rte_mempool *mp,
+ unsigned int n)
+{
+ unsigned int len;
+
+ RTE_ASSERT(cache != NULL);
+ RTE_ASSERT(mp != NULL);
+
+ rte_mempool_trace_cache_zc_get_bulk(cache, mp, n);
+
+ len = cache->len;
+
+ if (n <= len) {
+ /* The request can be satisfied from the cache as is. */
+ len -= n;
+ } else if (likely(n <= cache->flushthresh)) {
+ /*
+ * The request itself can be satisfied from the cache.
+ * But first, the cache must be filled from the backend;
+ * fetch size + requested - len objects.
+ */
+ int ret;
+ const unsigned int size = cache->size;
+
+ ret = rte_mempool_ops_dequeue_bulk(mp, &cache->objs[len], size
+ n - len);
If size is RTE_MEMPOOL_CACHE_MAX_SIZE and n is cache->flushthres (i.e.
RTE_MEMPOOL_CACHE_MAX_SIZE * 1.5), we'll dequeue up to
RTE_MEMPOOL_CACHE_MAX_SIZE * 2.5 objects
whereas cache objects size is just
RTE_MEMPOOL_CACHE_MAX_SIZE * 2. Am I missing something?
+ if (unlikely(ret < 0)) {
+ /*
+ * We are buffer constrained.
+ * Do not fill the cache, just satisfy the request.
+ */
+ ret = rte_mempool_ops_dequeue_bulk(mp,
&cache->objs[len], n - len);
+ if (unlikely(ret < 0)) {
+ /* Unable to satisfy the request. */
+
+ RTE_MEMPOOL_STAT_ADD(mp, get_fail_bulk, 1);
+ RTE_MEMPOOL_STAT_ADD(mp, get_fail_objs, n);
+
+ rte_errno = -ret;
+ return NULL;
+ }
+
+ len = 0;
+ } else
+ len = size;
Curly brackets are required in else branch since if branch
above has curly brackets.
+ } else {
+ /* The request itself is too big for the cache. */
+ rte_errno = EINVAL;
+ return NULL;
+ }
+
+ cache->len = len;
+
+ RTE_MEMPOOL_CACHE_STAT_ADD(cache, get_success_bulk, 1);
+ RTE_MEMPOOL_CACHE_STAT_ADD(cache, get_success_objs, n);
+
+ return &cache->objs[len];
+}
+
/**
* @internal Put several objects back in the mempool; used internally.
* @param mp
