v6 changes: reflect the changes in release notes and library version map file revise our duff's code style a bit to make it more readable
v5 changes: add comment about duff's device and our variant implementation v3 changes: move while after case 0 add context about duff's device and why we use while loop in the commit message v2 changes: unroll the loop a bit to help the performance rte_pktmbuf_alloc_bulk allocates a bulk of packet mbufs. There is related thread about this bulk API. http://dpdk.org/dev/patchwork/patch/4718/ Thanks to Konstantin's loop unrolling. Attached the wiki page about duff's device. It explains the performance optimization through loop unwinding, and also the most dramatic use of case label fall-through. https://en.wikipedia.org/wiki/Duff%27s_device In our implementation, we use while() loop rather than do{} while() loop because we could not assume count is strictly positive. Using while() loop saves one line of check if count is zero. Signed-off-by: Gerald Rogers <gerald.rogers at intel.com> Signed-off-by: Huawei Xie <huawei.xie at intel.com> Acked-by: Konstantin Ananyev <konstantin.ananyev at intel.com> --- doc/guides/rel_notes/release_2_3.rst | 3 ++ lib/librte_mbuf/rte_mbuf.h | 55 ++++++++++++++++++++++++++++++++++++ lib/librte_mbuf/rte_mbuf_version.map | 7 +++++ 3 files changed, 65 insertions(+) diff --git a/doc/guides/rel_notes/release_2_3.rst b/doc/guides/rel_notes/release_2_3.rst index 99de186..a52cba3 100644 --- a/doc/guides/rel_notes/release_2_3.rst +++ b/doc/guides/rel_notes/release_2_3.rst @@ -4,6 +4,9 @@ DPDK Release 2.3 New Features ------------ +* **Enable bulk allocation of mbufs. ** + A new function ``rte_pktmbuf_alloc_bulk()`` has been added to allow the user + to allocate a bulk of mbufs. Resolved Issues --------------- diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h index f234ac9..b2ed479 100644 --- a/lib/librte_mbuf/rte_mbuf.h +++ b/lib/librte_mbuf/rte_mbuf.h @@ -1336,6 +1336,61 @@ static inline struct rte_mbuf *rte_pktmbuf_alloc(struct rte_mempool *mp) } /** + * Allocate a bulk of mbufs, initialize refcnt and reset the fields to default + * values. + * + * @param pool + * The mempool from which mbufs are allocated. + * @param mbufs + * Array of pointers to mbufs + * @param count + * Array size + * @return + * - 0: Success + */ +static inline int rte_pktmbuf_alloc_bulk(struct rte_mempool *pool, + struct rte_mbuf **mbufs, unsigned count) +{ + unsigned idx = 0; + int rc; + + rc = rte_mempool_get_bulk(pool, (void **)mbufs, count); + if (unlikely(rc)) + return rc; + + /* To understand duff's device on loop unwinding optimization, see + * https://en.wikipedia.org/wiki/Duff's_device. + * Here while() loop is used rather than do() while{} to avoid extra + * check if count is zero. + */ + switch (count % 4) { + case 0: + while (idx != count) { + RTE_MBUF_ASSERT(rte_mbuf_refcnt_read(mbufs[idx]) == 0); + rte_mbuf_refcnt_set(mbufs[idx], 1); + rte_pktmbuf_reset(mbufs[idx]); + idx++; + case 3: + RTE_MBUF_ASSERT(rte_mbuf_refcnt_read(mbufs[idx]) == 0); + rte_mbuf_refcnt_set(mbufs[idx], 1); + rte_pktmbuf_reset(mbufs[idx]); + idx++; + case 2: + RTE_MBUF_ASSERT(rte_mbuf_refcnt_read(mbufs[idx]) == 0); + rte_mbuf_refcnt_set(mbufs[idx], 1); + rte_pktmbuf_reset(mbufs[idx]); + idx++; + case 1: + RTE_MBUF_ASSERT(rte_mbuf_refcnt_read(mbufs[idx]) == 0); + rte_mbuf_refcnt_set(mbufs[idx], 1); + rte_pktmbuf_reset(mbufs[idx]); + idx++; + } + } + return 0; +} + +/** * Attach packet mbuf to another packet mbuf. * * After attachment we refer the mbuf we attached as 'indirect', diff --git a/lib/librte_mbuf/rte_mbuf_version.map b/lib/librte_mbuf/rte_mbuf_version.map index e10f6bd..257c65a 100644 --- a/lib/librte_mbuf/rte_mbuf_version.map +++ b/lib/librte_mbuf/rte_mbuf_version.map @@ -18,3 +18,10 @@ DPDK_2.1 { rte_pktmbuf_pool_create; } DPDK_2.0; + +DPDK_2.3 { + global: + + rte_pktmbuf_alloc_bulk; + +} DPDK_2.1; -- 1.8.1.4
