Re: [PATCH 1/2] ACPI / hotplug / PCI: Avoid doing too much forspurious notifies

[Yinghai Lu]

On Fri, Sep 6, 2013 at 6:43 AM, Rafael J. Wysocki <rjw@xxxxxxx> wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
>
> Sometimes we may get a spurious device check or bus check notify for
> a hotplug device and in those cases we should avoid doing all of the
> configuration work needed when something actually changes.  To that
> end, check the return value of pci_scan_slot() in enable_slot() and
> bail out early if it is 0.
>
> This turns out to help reduce the amount of diagnostic output from
> the ACPIPHP subsystem and speed up boot on at least one system that
> generates multiple device check notifies for PCIe ports during
> boot.
>
> Reported-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> ---
>  drivers/pci/hotplug/acpiphp_glue.c |   35 +++++++++++++++++++++++++++--------
>  1 file changed, 27 insertions(+), 8 deletions(-)
>
> Index: linux-pm/drivers/pci/hotplug/acpiphp_glue.c
> ===================================================================
> --- linux-pm.orig/drivers/pci/hotplug/acpiphp_glue.c
> +++ linux-pm/drivers/pci/hotplug/acpiphp_glue.c
> @@ -542,12 +542,12 @@ static void __ref enable_slot(struct acp
>         struct acpiphp_func *func;
>         int max, pass;
>         LIST_HEAD(add_list);
> +       int nr_found;
>
>         list_for_each_entry(func, &slot->funcs, sibling)
>                 acpiphp_bus_add(func_to_handle(func));
>
> -       pci_scan_slot(bus, PCI_DEVFN(slot->device, 0));
> -
> +       nr_found = pci_scan_slot(bus, PCI_DEVFN(slot->device, 0));
>         max = acpiphp_max_busnr(bus);
>         for (pass = 0; pass < 2; pass++) {
>                 list_for_each_entry(dev, &bus->devices, bus_list) {
> @@ -566,8 +566,11 @@ static void __ref enable_slot(struct acp
>                         }
>                 }
>         }
> -
>         __pci_bus_assign_resources(bus, &add_list, NULL);
> +       /* Nothing more to do here if there are no new devices on this bus. */
> +       if (!nr_found && (slot->flags & SLOT_ENABLED))
> +               return;
> +
>         acpiphp_sanitize_bus(bus);
>         acpiphp_set_hpp_values(bus);
>         acpiphp_set_acpi_region(slot);
>

why not just returning early before size bridges and assign unassign resources?

Yinghai
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/