[dpdk-dev] [PATCH v3 5/6] net/mlx4: add control of excessive memory pinning by kernel

[Yongseok Koh <yskoh@mellanox.com>]

A new PMD parameter (mr_ext_memseg_en) is added to control extension of
memseg when creating a MR. It is enabled by default.

If enabled, mlx4_mr_create() tries to maximize the range of MR
registration so that the LKey lookup tables on datapath become smaller and
get the best performance. However, it may worsen memory utilization
because registered memory is pinned by kernel driver. Even if a page in the
extended chunk is freed, that doesn't become reusable until the entire
memory is freed and the MR is destroyed.

To make freed pages available immediately, this parameter has to be turned
off but it could drop performance.

Signed-off-by: Yongseok Koh <yskoh@mellanox.com>
Acked-by: Shahaf Shuler <shahafs@mellanox.com>
---
 doc/guides/nics/mlx4.rst   | 11 +++++++++++
 drivers/net/mlx4/mlx4.c    | 11 +++++++++--
 drivers/net/mlx4/mlx4.h    |  5 +++++
 drivers/net/mlx4/mlx4_mr.c | 20 +++++++++++++++-----
 4 files changed, 40 insertions(+), 7 deletions(-)

diff --git a/doc/guides/nics/mlx4.rst b/doc/guides/nics/mlx4.rst
index cd34838f41..c8a02be4dd 100644
--- a/doc/guides/nics/mlx4.rst
+++ b/doc/guides/nics/mlx4.rst
@@ -119,6 +119,17 @@ Run-time configuration
   times for additional ports. All ports are probed by default if left
   unspecified.
 
+- ``mr_ext_memseg_en`` parameter [int]
+
+  A nonzero value enables extending memseg when registering DMA memory. If
+  enabled, the number of entries in MR (Memory Region) lookup table on datapath
+  is minimized and it benefits performance. On the other hand, it worsens memory
+  utilization because registered memory is pinned by kernel driver. Even if a
+  page in the extended chunk is freed, that doesn't become reusable until the
+  entire memory is freed.
+
+  Enabled by default.
+
 Kernel module parameters
 ~~~~~~~~~~~~~~~~~~~~~~~~
 
diff --git a/drivers/net/mlx4/mlx4.c b/drivers/net/mlx4/mlx4.c
index 315640a6d7..252658fc6a 100644
--- a/drivers/net/mlx4/mlx4.c
+++ b/drivers/net/mlx4/mlx4.c
@@ -66,11 +66,14 @@ struct mlx4_conf {
 		uint32_t present; /**< Bit-field for existing ports. */
 		uint32_t enabled; /**< Bit-field for user-enabled ports. */
 	} ports;
+	int mr_ext_memseg_en;
+	/** Whether memseg should be extended for MR creation. */
 };
 
 /* Available parameters list. */
 const char *pmd_mlx4_init_params[] = {
 	MLX4_PMD_PORT_KVARG,
+	MLX4_MR_EXT_MEMSEG_EN_KVARG,
 	NULL,
 };
 
@@ -509,6 +512,8 @@ mlx4_arg_parse(const char *key, const char *val, struct mlx4_conf *conf)
 			return -rte_errno;
 		}
 		conf->ports.enabled |= 1 << tmp;
+	} else if (strcmp(MLX4_MR_EXT_MEMSEG_EN_KVARG, key) == 0) {
+		conf->mr_ext_memseg_en = !!tmp;
 	} else {
 		rte_errno = EINVAL;
 		WARN("%s: unknown parameter", key);
@@ -544,10 +549,10 @@ mlx4_args(struct rte_devargs *devargs, struct mlx4_conf *conf)
 	}
 	/* Process parameters. */
 	for (i = 0; pmd_mlx4_init_params[i]; ++i) {
-		arg_count = rte_kvargs_count(kvlist, MLX4_PMD_PORT_KVARG);
+		arg_count = rte_kvargs_count(kvlist, pmd_mlx4_init_params[i]);
 		while (arg_count-- > 0) {
 			ret = rte_kvargs_process(kvlist,
-						 MLX4_PMD_PORT_KVARG,
+						 pmd_mlx4_init_params[i],
 						 (int (*)(const char *,
 							  const char *,
 							  void *))
@@ -876,6 +881,7 @@ mlx4_pci_probe(struct rte_pci_driver *pci_drv, struct rte_pci_device *pci_dev)
 	struct ibv_device_attr_ex device_attr_ex;
 	struct mlx4_conf conf = {
 		.ports.present = 0,
+		.mr_ext_memseg_en = 1,
 	};
 	unsigned int vf;
 	int i;
@@ -1100,6 +1106,7 @@ mlx4_pci_probe(struct rte_pci_driver *pci_drv, struct rte_pci_device *pci_dev)
 					device_attr_ex.tso_caps.max_tso;
 		DEBUG("TSO is %ssupported",
 		      priv->tso ? "" : "not ");
+		priv->mr_ext_memseg_en = conf.mr_ext_memseg_en;
 		/* Configure the first MAC address by default. */
 		err = mlx4_get_mac(priv, &mac.addr_bytes);
 		if (err) {
diff --git a/drivers/net/mlx4/mlx4.h b/drivers/net/mlx4/mlx4.h
index 1a7b1fb541..4ff98d772b 100644
--- a/drivers/net/mlx4/mlx4.h
+++ b/drivers/net/mlx4/mlx4.h
@@ -53,6 +53,9 @@
 /** Port parameter. */
 #define MLX4_PMD_PORT_KVARG "port"
 
+/** Enable extending memsegs when creating a MR. */
+#define MLX4_MR_EXT_MEMSEG_EN_KVARG "mr_ext_memseg_en"
+
 /* Reserved address space for UAR mapping. */
 #define MLX4_UAR_SIZE (1ULL << (sizeof(uintptr_t) * 4))
 
@@ -165,6 +168,8 @@ struct mlx4_priv {
 	uint32_t hw_csum_l2tun:1; /**< Checksum support for L2 tunnels. */
 	uint32_t hw_fcs_strip:1; /**< FCS stripping toggling is supported. */
 	uint32_t tso:1; /**< Transmit segmentation offload is supported. */
+	uint32_t mr_ext_memseg_en:1;
+	/** Whether memseg should be extended for MR creation. */
 	uint32_t tso_max_payload_sz; /**< Max supported TSO payload size. */
 	uint32_t hw_rss_max_qps; /**< Max Rx Queues supported by RSS. */
 	uint64_t hw_rss_sup; /**< Supported RSS hash fields (Verbs format). */
diff --git a/drivers/net/mlx4/mlx4_mr.c b/drivers/net/mlx4/mlx4_mr.c
index 0ba55fda04..6db917a092 100644
--- a/drivers/net/mlx4/mlx4_mr.c
+++ b/drivers/net/mlx4/mlx4_mr.c
@@ -580,14 +580,24 @@ mlx4_mr_create(struct rte_eth_dev *dev, struct mlx4_mr_cache *entry,
 	 */
 	mlx4_mr_garbage_collect(dev);
 	/*
-	 * Find out a contiguous virtual address chunk in use, to which the
-	 * given address belongs, in order to register maximum range. In the
-	 * best case where mempools are not dynamically recreated and
+	 * If enabled, find out a contiguous virtual address chunk in use, to
+	 * which the given address belongs, in order to register maximum range.
+	 * In the best case where mempools are not dynamically recreated and
 	 * '--socket-mem' is specified as an EAL option, it is very likely to
 	 * have only one MR(LKey) per a socket and per a hugepage-size even
-	 * though the system memory is highly fragmented.
+	 * though the system memory is highly fragmented. As the whole memory
+	 * chunk will be pinned by kernel, it can't be reused unless entire
+	 * chunk is freed from EAL.
+	 *
+	 * If disabled, just register one memseg (page). Then, memory
+	 * consumption will be minimized but it may drop performance if there
+	 * are many MRs to lookup on the datapath.
 	 */
-	if (!rte_memseg_contig_walk(mr_find_contig_memsegs_cb, &data)) {
+	if (!priv->mr_ext_memseg_en) {
+		data.msl = rte_mem_virt2memseg_list((void *)addr);
+		data.start = RTE_ALIGN_FLOOR(addr, data.msl->page_sz);
+		data.end = data.start + data.msl->page_sz;
+	} else if (!rte_memseg_contig_walk(mr_find_contig_memsegs_cb, &data)) {
 		WARN("port %u unable to find virtually contiguous"
 		     " chunk for address (%p)."
 		     " rte_memseg_contig_walk() failed.",
-- 
2.11.0