[dpdk-dev] [PATCH] common/mlx5: fix CPU detection for PCI relaxed ordering

[Thomas Monjalon <thomas@monjalon.net>]

The detection of the CPU was done in a constructor and shared
in a global variable.

This variable may not be visible in the net PMD
because it was not exported as part of the .map file.
It is fixed by exporting a function, which is cleaner than a variable.

By checking the CPU only at the first call of the function,
doing the check in a constructor becomes useless.
Note: the priority of the constructor was probably irrelevant.

At the same time, the comments are reworded or dropped if useless.

Fixes: 4c204fe5e5d2 ("common/mlx5: disable relaxed ordering in unsuitable CPUs")
Cc: shirik@mellanox.com
Cc: stable@dpdk.org

Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
---
 drivers/common/mlx5/linux/mlx5_common_verbs.c |  2 +-
 drivers/common/mlx5/mlx5_common.c             | 53 ++++++++-----------
 drivers/common/mlx5/mlx5_common.h             |  4 +-
 .../common/mlx5/rte_common_mlx5_version.map   |  2 +
 drivers/net/mlx5/mlx5_flow_dv.c               |  2 +-
 5 files changed, 28 insertions(+), 35 deletions(-)

diff --git a/drivers/common/mlx5/linux/mlx5_common_verbs.c b/drivers/common/mlx5/linux/mlx5_common_verbs.c
index a2fc7a36bd..31ac20fe09 100644
--- a/drivers/common/mlx5/linux/mlx5_common_verbs.c
+++ b/drivers/common/mlx5/linux/mlx5_common_verbs.c
@@ -55,7 +55,7 @@ mlx5_common_verbs_reg_mr(void *pd, void *addr, size_t length,
 	memset(pmd_mr, 0, sizeof(*pmd_mr));
 	ibv_mr = mlx5_glue->reg_mr(pd, addr, length,
 				   IBV_ACCESS_LOCAL_WRITE |
-				   (haswell_broadwell_cpu ? 0 :
+				   (mlx5_cpu_is_haswell_broadwell() ? 0 :
 				   IBV_ACCESS_RELAXED_ORDERING));
 	if (!ibv_mr)
 		return -1;
diff --git a/drivers/common/mlx5/mlx5_common.c b/drivers/common/mlx5/mlx5_common.c
index 693e2c68c8..7232d5131d 100644
--- a/drivers/common/mlx5/mlx5_common.c
+++ b/drivers/common/mlx5/mlx5_common.c
@@ -20,8 +20,6 @@ int mlx5_common_logtype;
 const struct mlx5_glue *mlx5_glue;
 #endif
 
-uint8_t haswell_broadwell_cpu;
-
 static int
 mlx5_class_check_handler(__rte_unused const char *key, const char *value,
 			 void *opaque)
@@ -59,19 +57,8 @@ mlx5_class_get(struct rte_devargs *devargs)
 }
 
 
-/* In case this is an x86_64 intel processor to check if
- * we should use relaxed ordering.
- */
 #ifdef RTE_ARCH_X86_64
-/**
- * This function returns processor identification and feature information
- * into the registers.
- *
- * @param eax, ebx, ecx, edx
- *		Pointers to the registers that will hold cpu information.
- * @param level
- *		The main category of information returned.
- */
+/* Processor identification and feature information filled in registers. */
 static inline void mlx5_cpu_id(unsigned int level,
 				unsigned int *eax, unsigned int *ebx,
 				unsigned int *ecx, unsigned int *edx)
@@ -97,17 +84,7 @@ RTE_INIT_PRIO(mlx5_glue_init, CLASS)
 	mlx5_glue_constructor();
 }
 
-/**
- * This function is responsible of initializing the variable
- *  haswell_broadwell_cpu by checking if the cpu is intel
- *  and reading the data returned from mlx5_cpu_id().
- *  since haswell and broadwell cpus don't have improved performance
- *  when using relaxed ordering we want to check the cpu type before
- *  before deciding whether to enable RO or not.
- *  if the cpu is haswell or broadwell the variable will be set to 1
- *  otherwise it will be 0.
- */
-RTE_INIT_PRIO(mlx5_is_haswell_broadwell_cpu, LOG)
+static bool mlx5_x86_is_haswell_broadwell(void)
 {
 #ifdef RTE_ARCH_X86_64
 	unsigned int broadwell_models[4] = {0x3d, 0x47, 0x4F, 0x56};
@@ -125,8 +102,7 @@ RTE_INIT_PRIO(mlx5_is_haswell_broadwell_cpu, LOG)
 	vendor = ebx;
 	max_level = eax;
 	if (max_level < 1) {
-		haswell_broadwell_cpu = 0;
-		return;
+		return false;
 	}
 	mlx5_cpu_id(1, &eax, &ebx, &ecx, &edx);
 	model = (eax >> 4) & 0x0f;
@@ -140,18 +116,31 @@ RTE_INIT_PRIO(mlx5_is_haswell_broadwell_cpu, LOG)
 		if (brand_id == 0 && family == 0x6) {
 			for (i = 0; i < RTE_DIM(broadwell_models); i++)
 				if (model == broadwell_models[i]) {
-					haswell_broadwell_cpu = 1;
-					return;
+					return true;
 				}
 			for (i = 0; i < RTE_DIM(haswell_models); i++)
 				if (model == haswell_models[i]) {
-					haswell_broadwell_cpu = 1;
-					return;
+					return true;
 				}
 		}
 	}
 #endif
-	haswell_broadwell_cpu = 0;
+	return false;
+}
+
+/*
+ * Check if the CPU is Intel Haswell or Broadwell,
+ * because PCI relaxed ordering has no performance benefit with these CPUs.
+ */
+bool mlx5_cpu_is_haswell_broadwell(void)
+{
+	static bool haswell_broadwell_cpu;
+	static bool once = false;
+
+	if (once)
+		return haswell_broadwell_cpu;
+	once = true;
+	return haswell_broadwell_cpu = mlx5_x86_is_haswell_broadwell();
 }
 
 /**
diff --git a/drivers/common/mlx5/mlx5_common.h b/drivers/common/mlx5/mlx5_common.h
index 2851507058..d453e0b3d8 100644
--- a/drivers/common/mlx5/mlx5_common.h
+++ b/drivers/common/mlx5/mlx5_common.h
@@ -243,6 +243,9 @@ struct mlx5_klm {
 
 LIST_HEAD(mlx5_dbr_page_list, mlx5_devx_dbr_page);
 
+__rte_internal
+bool mlx5_cpu_is_haswell_broadwell(void);
+
 __rte_internal
 enum mlx5_class mlx5_class_get(struct rte_devargs *devargs);
 __rte_internal
@@ -255,6 +258,5 @@ int64_t mlx5_get_dbr(void *ctx,  struct mlx5_dbr_page_list *head,
 __rte_internal
 int32_t mlx5_release_dbr(struct mlx5_dbr_page_list *head, uint32_t umem_id,
 			 uint64_t offset);
-extern uint8_t haswell_broadwell_cpu;
 
 #endif /* RTE_PMD_MLX5_COMMON_H_ */
diff --git a/drivers/common/mlx5/rte_common_mlx5_version.map b/drivers/common/mlx5/rte_common_mlx5_version.map
index ae57ebdba5..501b9fff3b 100644
--- a/drivers/common/mlx5/rte_common_mlx5_version.map
+++ b/drivers/common/mlx5/rte_common_mlx5_version.map
@@ -6,6 +6,8 @@ INTERNAL {
 	mlx5_common_verbs_reg_mr;
 	mlx5_common_verbs_dereg_mr;
 
+	mlx5_cpu_is_haswell_broadwell;
+
 	mlx5_create_mr_ext;
 
 	mlx5_dev_to_pci_addr;
diff --git a/drivers/net/mlx5/mlx5_flow_dv.c b/drivers/net/mlx5/mlx5_flow_dv.c
index 8b5b6838fa..f1109ae095 100644
--- a/drivers/net/mlx5/mlx5_flow_dv.c
+++ b/drivers/net/mlx5/mlx5_flow_dv.c
@@ -4201,7 +4201,7 @@ flow_dv_create_counter_stat_mem_mng(struct rte_eth_dev *dev, int raws_n)
 	mkey_attr.klm_num = 0;
 	if (priv->config.hca_attr.relaxed_ordering_write &&
 		priv->config.hca_attr.relaxed_ordering_read  &&
-		!haswell_broadwell_cpu)
+		!mlx5_cpu_is_haswell_broadwell())
 		mkey_attr.relaxed_ordering = 1;
 	mem_mng->dm = mlx5_devx_cmd_mkey_create(sh->ctx, &mkey_attr);
 	if (!mem_mng->dm) {
-- 
2.27.0