This requirement came from ODP-OVS: it handles buffers through 'struct ofpbuf'
(in upstream it became 'struct dp_packet'), and they can be non-ODP buffers as
well. Therefore after receiving a packet currently we have to reset three
fields in it: 'source' (to ODP), 'allocated' (segment size, OVS doesn't support
multiple segments in this struct) and 'odp_pkt' (points to the containing
odp_packet_t)
The native DPDK implementation takes advantage of the fact that the buffer and
user metadata area, where this struct is stored is allocated during pool
creation time, therefore it initializes it to static values at startup. When
I've tried this behaviour with ODP-DPDK, the performance increased from ~12.7
to ~12.9 Mpp. That's only ~%1.6 increase, but in other words it's ~%17 of the
gap between the current and OVS-DPDK performance (13.9 Mpp)
I would like a propose an optional feature where the implementation can signal
if it guarantees this behaviour. I think most implementations would
preallocate these areas to achieve good performance, but e.g. linux-generic
does not AFAIK.
Signed-off-by: Zoltan Kiss <zoltan.k...@linaro.org>
---
include/odp/api/config.h | 10 ++++++++++
include/odp/api/packet.h | 4 +++-
2 files changed, 13 insertions(+), 1 deletion(-)
diff --git a/include/odp/api/config.h b/include/odp/api/config.h
index 91ea34e..d48030e 100644
--- a/include/odp/api/config.h
+++ b/include/odp/api/config.h
@@ -121,6 +121,16 @@ extern "C" {
*/
#define ODP_CONFIG_PACKET_BUF_LEN_MAX (ODP_CONFIG_PACKET_SEG_LEN_MIN*6)
+/**
+ * Guarantee that user metadata is allocated during pool creation
+ *
+ * If this parameter is 1, applications can avoid reseting persistent parts of
+ * the area returned by odp_packet_user_area() by setting them once, after pool
+ * creation. It will keep its content between odp_packet_free() and
+ * odp_packet_alloc().
+ */
+#define ODP_CONFIG_PACKET_PERSISTENT_MD 0
+
/** Maximum number of shared memory blocks.
*
* This the the number of separate SHM areas that can be reserved concurrently
diff --git a/include/odp/api/packet.h b/include/odp/api/packet.h
index 91a124a..d7aeb95 100644
--- a/include/odp/api/packet.h
+++ b/include/odp/api/packet.h
@@ -448,7 +448,9 @@ void odp_packet_user_ptr_set(odp_packet_t pkt, const void
*ctx);
* User area address
*
* Each packet has an area for user data. Size of the area is fixed and defined
- * in packet pool parameters.
+ * in packet pool parameters. If ODP_CONFIG_PACKET_PERSISTENT_MD is 1, this
+ * area is allocated during pool creation, and keep its content between
+ * odp_packet_free() and odp_packet_alloc().
*
* @param pkt Packet handle
*
--
1.9.1
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