On 24.05.2017 17:44, Greg KH wrote:
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?
Last minute doubt, nothing should be wrong, but I started to wonder if there is
any particular reason the ACPI part was done the way it was.
Or if maybe other drivers could benefit from checking cached _ADR value first as
well, and this whole thing should be a part of drivers/acpi/glue.c instead?
(adding acpi mailing list, not just Rafael)
Thanks
-Mathias
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