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
