2018-06-27 18:34 GMT+02:00 Ferruh Yigit [off-list ref]:

On 4/11/2018 3:07 PM, Rafal Kozik wrote:

quoted

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

Parameter wc_activate add possibility to enable it for
those PMD that could support it.

Signed-off-by: Rafal Kozik <redacted>

Hi Rafal,

First, sorry for delayed comment.

quoted

---
 kernel/linux/igb_uio/igb_uio.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/kernel/linux/igb_uio/igb_uio.c b/kernel/linux/igb_uio/igb_uio.c
index 4cae4dd..42e3b3f 100644
--- a/kernel/linux/igb_uio/igb_uio.c
+++ b/kernel/linux/igb_uio/igb_uio.c

@@ -30,6 +30,7 @@ struct rte_uio_pci_dev {
      int refcnt;
 };

+static int wc_activate;
 static char *intr_mode;
 static enum rte_intr_mode igbuio_intr_mode_preferred = RTE_INTR_MODE_MSIX;
 /* sriov sysfs */

@@ -375,9 +376,13 @@ igbuio_pci_setup_iomem(struct pci_dev *dev, struct uio_info *info,
      len = pci_resource_len(dev, pci_bar);
      if (addr == 0 || len == 0)
              return -1;
-     internal_addr = ioremap(addr, len);
-     if (internal_addr == NULL)
-             return -1;
+     if (wc_activate == 0) {
+             internal_addr = ioremap(addr, len);
+             if (internal_addr == NULL)
+                     return -1;
+     } else {
+             internal_addr = NULL;
+     }

Why we need this update at all?
What is the relation between internal_address and write combined?

As far as I can see we are not using internal_addr at all, what do you observe
in write combined usage without this modification?

To get internal_addr memory need to be mapped. But as memory could not be
mapped twice: with and without WC it should be skipped for WC. [1]
WC does not work without this modification.

[1] https://www.kernel.org/doc/ols/2008/ols2008v2-pages-135-144.pdf
        section 5.3 and 5.4

quoted

      info->mem[n].name = name;
      info->mem[n].addr = addr;
      info->mem[n].internal_addr = internal_addr;

@@ -638,6 +643,12 @@ MODULE_PARM_DESC(intr_mode,
 "    " RTE_INTR_MODE_LEGACY_NAME "     Use Legacy interrupt\n"
 "\n");

+module_param(wc_activate, int, 0);
+MODULE_PARM_DESC(wc_activate,
+"Activate support for write combining (WC) (default=0)\n"
+"    0 - disable\n"
+"    other - enable\n");
+
 MODULE_DESCRIPTION("UIO driver for Intel IGB PCI cards");
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Intel Corporation");