Olivier, David,
could you take a look at naming suggested below and share your thoughts.
My fear is that rte_mbuf_buf_addr() is too generic and true for direct mbuf
only. That's why I'd like to highlight it in the function name.
Thanks,
Andrew.
On 1/11/19 2:03 PM, Yongseok Koh wrote:
On Fri, Jan 11, 2019 at 11:14:22AM +0300, Andrew Rybchenko wrote:
On 1/10/19 9:35 PM, Yongseok Koh wrote:
This patch introduces two new functions - rte_mbuf_buf_addr() and
rte_mbuf_data_addr_default().
rte_mbuf_buf_addr() reutrns the default buffer address of given mbuf which
comes after mbuf structure and private data.
rte_mbuf_data_addr_default() returns the default address of mbuf data
taking the headroom into account.
Signed-off-by: Yongseok Koh <ys...@mellanox.com>
---
v3:
* rename functions
v2:
* initial implementation
lib/librte_mbuf/rte_mbuf.h | 43 ++++++++++++++++++++++++++++++++++++++++---
1 file changed, 40 insertions(+), 3 deletions(-)
diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
index bc562dc8a9..486566fc28 100644
--- a/lib/librte_mbuf/rte_mbuf.h
+++ b/lib/librte_mbuf/rte_mbuf.h
@@ -788,8 +788,47 @@ rte_mbuf_from_indirect(struct rte_mbuf *mi)
}
/**
+ * Return the default buffer address of the mbuf.
+ *
+ * @param mb
+ * The pointer to the mbuf.
+ * @param mp
+ * The pointer to the mempool of the mbuf.
+ * @return
+ * The pointer of the mbuf buffer.
+ */
+static inline char * __rte_experimental
+rte_mbuf_buf_addr(struct rte_mbuf *mb, struct rte_mempool *mp)
struct rte_mbuf has pool member. So, I don't understand why mp
argument is required. I guess there is a reason, but it should be
explained in comments. I see motivation in rte_mbuf_to_baddr()
description, but rte_mbuf_buf_add() does not explain it.
Well, I don't like to put same comment here and there but I'll add small comment
here.
Also right now the function name looks like simple get accessor for
buf_addr and I'd expect to seem one line implementation may be
with extra debug checks: return mb->buf_addr.
This func is suggested by David and Olivier because same code is being repeated
in multiple locations. This can be used to initialize a mbuf when mb->buf_addr
is
null. And second use-case (this is my use-case) is to get the buf_addr without
accessing the mbuf struct when mempool of mbuf is known, e.g. Rx buffer
replenishment. It is definitely beneficial for performance, especially RISC
cores.
May be rte_mbuf_direct_buf_addr() ?
If so, similar below rte_mbuf_direct_data_addr_default().
Regarding naming, people have different tastes. As it is acked by Olivier and
David, I'll keep the names.
Thanks,
Yongseok
+{
+ char *buffer_addr;
+
+ buffer_addr = (char *)mb + sizeof(*mb) + rte_pktmbuf_priv_size(mp);
+ return buffer_addr;
+}
+
+
+/**
+ * Return the default address of the beginning of the mbuf data.
+ *
+ * @param mb
+ * The pointer to the mbuf.
+ * @return
+ * The pointer of the beginning of the mbuf data.
+ */
+static inline char * __rte_experimental
+rte_mbuf_data_addr_default(struct rte_mbuf *mb)
+{
+ return rte_mbuf_buf_addr(mb, mb->pool) + RTE_PKTMBUF_HEADROOM;
+}
+
+/**
* Return the buffer address embedded in the given mbuf.
*
+ * Note that accessing mempool pointer of a mbuf is expensive because the
+ * pointer is stored in the 2nd cache line of mbuf. If mempool is known, it
+ * is better not to reference the mempool pointer in mbuf but calling
+ * rte_mbuf_buf_addr() would be more efficient.
+ *
* @param md
* The pointer to the mbuf.
* @return
@@ -798,9 +837,7 @@ rte_mbuf_from_indirect(struct rte_mbuf *mi)
static inline char *
rte_mbuf_to_baddr(struct rte_mbuf *md)
{
- char *buffer_addr;
- buffer_addr = (char *)md + sizeof(*md) +
rte_pktmbuf_priv_size(md->pool);
- return buffer_addr;
+ return rte_mbuf_buf_addr(md, md->pool);
}
/**
