[dpdk-dev] [PATCH v6 1/2] mbuf: provide rte_pktmbuf_alloc_bulk API
Huawei Xie
huawei.xie at intel.com
Tue Jan 26 18:03:34 CET 2016
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
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