On Wed, May 24, 2017 at 04:11:12PM +0300, Mathias Nyman wrote: > This optimization significantly reduces xhci driver load time. > > In ACPI tables the acpi companion port devices are children of > the hub device. The port devices are identified by their port number > returned by the ACPI _ADR method. > _ADR 0 is reserved for the root hub device. > > The current implementation to find a acpi companion port device > loops through all acpi port devices under that parent hub, calling > their _ADR method each time a new port device is added. > > for a xHC controller with 25 ports under its roothub it > will end up invoking ACPI bytecode 625 times before all ports > are ready, making it really slow. > > The _ADR values are already read and cached earler. So instead of > running the bytecode again we can check the cached _ADR value first, > and then fall back to the old way. > > As one of the more significant changes, the xhci load time on > Intel kabylake reduced by 70%, (28ms) from > initcall xhci_pci_init+0x0/0x49 returned 0 after 39537 usecs > to > initcall xhci_pci_init+0x0/0x49 returned 0 after 11270 usecs > > Signed-off-by: Mathias Nyman <mathias.nyman@xxxxxxxxxxxxxxx> > --- > drivers/usb/core/usb-acpi.c | 26 +++++++++++++++++++++++--- > 1 file changed, 23 insertions(+), 3 deletions(-) Why is this RFC? What's wrong with it as-is? thanks, greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
