linux-kernel - Re: [PATCH 1/2] ACPI / hotplug / PCI: Avoid doing too much for spurious notifies

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Message-ID: <CAE9FiQXacWEXngMCQeB1CPVxuvL-jNW_MyMcDV-e8tK6DvY3Kw@mail.gmail.com>
Date:	Fri, 6 Sep 2013 08:46:28 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Alex Williamson <alex.williamson@...hat.com>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux PCI <linux-pci@...r.kernel.org>,
	Jiang Liu <liuj97@...il.com>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH 1/2] ACPI / hotplug / PCI: Avoid doing too much for
 spurious notifies

On Fri, Sep 6, 2013 at 6:43 AM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>
> 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@...hat.com>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
>  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
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