[dpdk-dev] [PATCH 0/4] support for write combining
Bruce Richardson
bruce.richardson at intel.com
Wed Apr 11 16:42:51 CEST 2018
On Wed, Apr 11, 2018 at 04:07:13PM +0200, Rafal Kozik wrote:
> Support for write combining.
>
> Rafal Kozik (4):
> igb_uio: add wc option
> bus/pci: reference driver structure
> eal: enable WC during resources mapping
> net/ena: enable WC
>
> drivers/bus/pci/linux/pci_uio.c | 39 ++++++++++++++++++++++++++++-----------
> drivers/bus/pci/pci_common.c | 13 ++++++++-----
> drivers/bus/pci/rte_bus_pci.h | 2 ++
> drivers/net/ena/ena_ethdev.c | 3 ++-
> kernel/linux/igb_uio/igb_uio.c | 17 ++++++++++++++---
> 5 files changed, 54 insertions(+), 20 deletions(-)
>
Couple of thoughts on this set.
You add an option to the kernel module to allow wc to be supported on a
device, but when we go to do PCI mapping, we either map the regular
resource file or the _wc one. Therefore:
1. Why not always have igb_uio support write-combining since it can be
controlled thereafter via userspace mapping one file or another?
2. Why not always map both resource and resource_wc files at the PCI level,
and make them available via different pointers to the driver? Then the
driver can choose at the per-access level which it wants to use. For
example, for init of a device, a driver may do all register access via
uncachable memory, and only use the write-combined support for
performance-critical parts. [I have a draft patch lying around here
somewhere that does something similar to that.]
One last question - if using vfio-pci kernel module, do the resource_wc
files present the bars as write-combined memory type, or are they
uncachable?
Regards,
/Bruce
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