Re: [dpdk-dev] [PATCH v4 1/4] igb_uio: add wc option

["Rafał Kozik" <rk@semihalf.com>]

> How can I confirm this silently fall-back behavior, is there any log can I turn
> on in kernel or anything from proc/sysfs?

I cannot find any.
I check it by measuring write speed.

2018-06-29 14:17 GMT+02:00 Rafal Kozik <rk@semihalf.com>:
> From: Kozik <rk@semihalf.com>
>
> Write combining (WC) increases NIC performance by making better
> utilization of PCI bus, but cannot be use by all PMD.
>
> 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]
>
> To do not spoil other drivers that potentially could use internal_addr,
> parameter wc_activate adds possibility to skip it for those PMDs,
> that do not use it.
>
> [1] https://www.kernel.org/doc/ols/2008/ols2008v2-pages-135-144.pdf
>         section 5.3 and 5.4
>
> Signed-off-by: Rafal Kozik <rk@semihalf.com>
> Acked-by: Bruce Richardson <bruce.richardson@intel.com>
> ---
>  kernel/linux/igb_uio/igb_uio.c | 18 +++++++++++++++---
>  1 file changed, 15 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/linux/igb_uio/igb_uio.c b/kernel/linux/igb_uio/igb_uio.c
> index b3233f1..e16e760 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 +376,14 @@ 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;
> +               pr_info("wc_activate is set\n");
> +       }
>         info->mem[n].name = name;
>         info->mem[n].addr = addr;
>         info->mem[n].internal_addr = internal_addr;
> @@ -650,6 +656,12 @@ 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");
> --
> 2.7.4
>