[dpdk-dev] [PATCH 3/4] eal: enable WC during resources mapping

[Rafal Kozik]

Write combining (wc) increase NIC performenca by making better
utilization of PCI bus, but cannot be used by all PMD.

It will be enable only if RTE_PCI_DRV_WC_ACTIVATE will be set in
drivers flags. For proper work also igb driver must be loaded with
wc_activate set to 1.

When mapping PCI resources firstly try to us wc.
If it is not supported it will fallback to normal mode.

Signed-off-by: Rafal Kozik <rk at semihalf.com>
---
 drivers/bus/pci/linux/pci_uio.c | 39 ++++++++++++++++++++++++++++-----------
 drivers/bus/pci/rte_bus_pci.h   |  2 ++
 2 files changed, 30 insertions(+), 11 deletions(-)

diff --git a/drivers/bus/pci/linux/pci_uio.c b/drivers/bus/pci/linux/pci_uio.c
index d423e4b..a1570c9 100644
--- a/drivers/bus/pci/linux/pci_uio.c
+++ b/drivers/bus/pci/linux/pci_uio.c
@@ -287,17 +287,14 @@ pci_uio_map_resource_by_index(struct rte_pci_device *dev, int res_idx,
 	void *mapaddr;
 	struct rte_pci_addr *loc;
 	struct pci_map *maps;
+	int wc_activate = 0;
+
+	if (dev->driver != NULL)
+		wc_activate = dev->driver->drv_flags & RTE_PCI_DRV_WC_ACTIVATE;
 
 	loc = &dev->addr;
 	maps = uio_res->maps;
 
-	/* update devname for mmap  */
-	snprintf(devname, sizeof(devname),
-			"%s/" PCI_PRI_FMT "/resource%d",
-			rte_pci_get_sysfs_path(),
-			loc->domain, loc->bus, loc->devid,
-			loc->function, res_idx);
-
 	/* allocate memory to keep path */
 	maps[map_idx].path = rte_malloc(NULL, strlen(devname) + 1, 0);
 	if (maps[map_idx].path == NULL) {
@@ -309,11 +306,31 @@ pci_uio_map_resource_by_index(struct rte_pci_device *dev, int res_idx,
 	/*
 	 * open resource file, to mmap it
 	 */
-	fd = open(devname, O_RDWR);
-	if (fd < 0) {
-		RTE_LOG(ERR, EAL, "Cannot open %s: %s\n",
+	if (wc_activate) {
+		/* update devname for mmap  */
+		snprintf(devname, sizeof(devname),
+			"%s/" PCI_PRI_FMT "/resource%d_wc",
+			rte_pci_get_sysfs_path(),
+			loc->domain, loc->bus, loc->devid,
+			loc->function, res_idx);
+
+		fd = open(devname, O_RDWR);
+	}
+
+	if (!wc_activate || fd < 0) {
+		snprintf(devname, sizeof(devname),
+			"%s/" PCI_PRI_FMT "/resource%d",
+			rte_pci_get_sysfs_path(),
+			loc->domain, loc->bus, loc->devid,
+			loc->function, res_idx);
+
+		/* then try to map resource file */
+		fd = open(devname, O_RDWR);
+		if (fd < 0) {
+			RTE_LOG(ERR, EAL, "Cannot open %s: %s\n",
 				devname, strerror(errno));
-		goto error;
+			goto error;
+		}
 	}
 
 	/* try mapping somewhere close to the end of hugepages */
diff --git a/drivers/bus/pci/rte_bus_pci.h b/drivers/bus/pci/rte_bus_pci.h
index 357afb9..b7bcce3 100644
--- a/drivers/bus/pci/rte_bus_pci.h
+++ b/drivers/bus/pci/rte_bus_pci.h
@@ -132,6 +132,8 @@ struct rte_pci_bus {
 
 /** Device needs PCI BAR mapping (done with either IGB_UIO or VFIO) */
 #define RTE_PCI_DRV_NEED_MAPPING 0x0001
+/** Device needs PCI BAR mapping with enabled write combining (wc) */
+#define RTE_PCI_DRV_WC_ACTIVATE 0x0002
 /** Device driver supports link state interrupt */
 #define RTE_PCI_DRV_INTR_LSC	0x0008
 /** Device driver supports device removal interrupt */
-- 
2.7.4