From: Olga Shern <ol...@mellanox.com>
Environment variable MLX5_PMD_ENABLE_PADDING enables HW packet padding
in PCI bus transactions.
When packet size is cache aligned and CRC stripping is enabled, 4 fewer
bytes are written to the PCI bus. Enabling padding makes such packets
aligned again.
In cases where PCI bandwidth is the bottleneck, padding can improve
performance by 10%.
This is disabled by default since this can also decrease performance for
unaligned packet sizes.
Signed-off-by: Olga Shern <olgas at mellanox.com>
---
doc/guides/nics/mlx5.rst | 14 ++++++++++++++
doc/guides/rel_notes/release_16_04.rst | 5 +++++
drivers/net/mlx5/Makefile | 5 +++++
drivers/net/mlx5/mlx5.c | 19 +++++++++++++++++++
drivers/net/mlx5/mlx5.h | 4 ++++
drivers/net/mlx5/mlx5_rxq.c | 10 ++++++++++
6 files changed, 57 insertions(+)
diff --git a/doc/guides/nics/mlx5.rst b/doc/guides/nics/mlx5.rst
index df07146..66fe0d9 100644
--- a/doc/guides/nics/mlx5.rst
+++ b/doc/guides/nics/mlx5.rst
@@ -155,6 +155,20 @@ Environment variables
lower performance when there is no backpressure, it is not enabled by
default.
+- ``MLX5_PMD_ENABLE_PADDING``
+
+ Enables HW packet padding in PCI bus transactions.
+
+ When packet size is cache aligned and CRC stripping is enabled, 4 fewer
+ bytes are written to the PCI bus. Enabling padding makes such packets
+ aligned again.
+
+ In cases where PCI bandwidth is the bottleneck, padding can improve
+ performance by 10%.
+
+ This is disabled by default since this can also decrease performance for
+ unaligned packet sizes.
+
Run-time configuration
~~~~~~~~~~~~~~~~~~~~~~
diff --git a/doc/guides/rel_notes/release_16_04.rst
b/doc/guides/rel_notes/release_16_04.rst
index 08f7592..a3a30fd 100644
--- a/doc/guides/rel_notes/release_16_04.rst
+++ b/doc/guides/rel_notes/release_16_04.rst
@@ -87,6 +87,11 @@ This section should contain new features added in this
release. Sample format:
Implemented TX support in secondary processes (like mlx4).
+* **mlx5: Added optional packet padding by HW.**
+
+ Added an option to make PCI bus transactions rounded to multiple of 64
+ bytes for better cache alignment.
+
Resolved Issues
---------------
diff --git a/drivers/net/mlx5/Makefile b/drivers/net/mlx5/Makefile
index 7076ae3..712c0a9 100644
--- a/drivers/net/mlx5/Makefile
+++ b/drivers/net/mlx5/Makefile
@@ -137,6 +137,11 @@ mlx5_autoconf.h: $(RTE_SDK)/scripts/auto-config-h.sh
infiniband/verbs.h \
enum IBV_EXP_CQ_RX_TCP_PACKET \
$(AUTOCONF_OUTPUT)
+ $Q sh -- '$<' '$@' \
+ HAVE_EXP_CREATE_WQ_FLAG_RX_END_PADDING \
+ infiniband/verbs.h \
+ enum IBV_EXP_CREATE_WQ_FLAG_RX_END_PADDING \
+ $(AUTOCONF_OUTPUT)
$(SRCS-$(CONFIG_RTE_LIBRTE_MLX5_PMD):.c=.o): mlx5_autoconf.h
diff --git a/drivers/net/mlx5/mlx5.c b/drivers/net/mlx5/mlx5.c
index 998e6f0..8baef28 100644
--- a/drivers/net/mlx5/mlx5.c
+++ b/drivers/net/mlx5/mlx5.c
@@ -68,6 +68,25 @@
#include "mlx5_defs.h"
/**
+ * Retrieve integer value from environment variable.
+ *
+ * @param[in] name
+ * Environment variable name.
+ *
+ * @return
+ * Integer value, 0 if the variable is not set.
+ */
+int
+mlx5_getenv_int(const char *name)
+{
+ const char *val = getenv(name);
+
+ if (val == NULL)
+ return 0;
+ return atoi(val);
+}
+
+/**
* DPDK callback to close the device.
*
* Destroy all queues and objects, free memory.
diff --git a/drivers/net/mlx5/mlx5.h b/drivers/net/mlx5/mlx5.h
index bad9283..436b70b 100644
--- a/drivers/net/mlx5/mlx5.h
+++ b/drivers/net/mlx5/mlx5.h
@@ -159,6 +159,10 @@ priv_unlock(struct priv *priv)
rte_spinlock_unlock(&priv->lock);
}
+/* mlx5.c */
+
+int mlx5_getenv_int(const char *);
+
/* mlx5_ethdev.c */
struct priv *mlx5_get_priv(struct rte_eth_dev *dev);
diff --git a/drivers/net/mlx5/mlx5_rxq.c b/drivers/net/mlx5/mlx5_rxq.c
index 3d84f41..0efa7a3 100644
--- a/drivers/net/mlx5/mlx5_rxq.c
+++ b/drivers/net/mlx5/mlx5_rxq.c
@@ -1258,6 +1258,16 @@ rxq_setup(struct rte_eth_dev *dev, struct rxq *rxq,
uint16_t desc,
0),
#endif /* HAVE_EXP_DEVICE_ATTR_VLAN_OFFLOADS */
};
+
+#ifdef HAVE_EXP_CREATE_WQ_FLAG_RX_END_PADDING
+ if (mlx5_getenv_int("MLX5_PMD_ENABLE_PADDING")) {
+ INFO("%p: packet padding is enabled on queue %p",
+ (void *)dev, (void *)rxq);
+ attr.wq.flags = IBV_EXP_CREATE_WQ_FLAG_RX_END_PADDING;
+ attr.wq.comp_mask |= IBV_EXP_CREATE_WQ_FLAGS;
+ }
+#endif /* HAVE_EXP_CREATE_WQ_FLAG_RX_END_PADDING */
+
tmpl.wq = ibv_exp_create_wq(priv->ctx, &attr.wq);
if (tmpl.wq == NULL) {
ret = (errno ? errno : EINVAL);
--
2.1.4
