linux-kernel - Re: [PATCH v3 11/12] PCI: Sort pci root bus resources list

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Date:	Tue, 3 Dec 2013 18:12:12 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Gu Zheng <guz.fnst@...fujitsu.com>,
	Guo Chao <yan@...ux.vnet.ibm.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 11/12] PCI: Sort pci root bus resources list

On Mon, Dec 2, 2013 at 3:11 PM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
> On Sat, Nov 30, 2013 at 3:40 PM, Yinghai Lu <yinghai@...nel.org> wrote:
>> Some x86 systems expose above 4G 64bit mmio in _CRS as non-pref mmio range.
>> [   49.415281] PCI host bridge to bus 0000:00
>> [   49.419921] pci_bus 0000:00: root bus resource [bus 00-1e]
>> [   49.426107] pci_bus 0000:00: root bus resource [io  0x0000-0x0cf7]
>> [   49.433041] pci_bus 0000:00: root bus resource [io  0x1000-0x5fff]
>> [   49.440010] pci_bus 0000:00: root bus resource [mem 0x000a0000-0x000bffff]
>> [   49.447768] pci_bus 0000:00: root bus resource [mem 0xfed8c000-0xfedfffff]
>> [   49.455532] pci_bus 0000:00: root bus resource [mem 0x90000000-0x9fffbfff]
>> [   49.463259] pci_bus 0000:00: root bus resource [mem 0x380000000000-0x381fffffffff]
>>
>> During assign unassigned 64bit mmio resource, it will go through
>> every non-pref mmio for root bus in pci_bus_alloc_resource().
>> As the loop is with pci_bus_for_each_resource(), and could have chance
>> to use under 4G mmio range instead of above 4G mmio range if the requested
>> range is not big enough, even it could handle above 4G 64bit pref mmio.
>>
>> For root bus, we can order list from high to low in pci_add_resource_offset(),
>> during creating root bus, it will still keep the same order in final bus
>> resource list.
>>         pci_acpi_scan_root
>>                 ==> add_resources
>>                         ==> pci_add_resource_offset: # Add to temp resources
>>                 ==> pci_create_root_bus
>>                         ==> pci_bus_add_resource # add to final bus resources.
>>
>> After that, we can make sure 64bit pref mmio for pci bridges will be allocated
>> higest of mmio non-pref, and in this case it is above 4G instead of under 4G.
>
> It really irritates me when I ask a question [1] and you just repost
> the patch without even trying to answer it.
>
> [1] http://lkml.kernel.org/r/CAErSpo4r6eJhgmfpth7haKDiKzDB+ZnEq0p_qdfTPo+kqySGgg@mail.gmail.com

I expanded the changelog quite a bit, and thought it should have
answered your concern.

The old nehalem-ex and westmere-ex platform have specify above 4g mmio as
pref, but new ivybridge-ex platform only keep above 4g mmio as mmio as non-pref.

so we need allocation code to try the above 4G range for pref
allocation at first to
avoid mmio pref taking under 4G mmio range.

We may need to backport it to old kernel or stable kernel, but should
wait a while after it get into linus's tree for a while.

Thanks

Yinghai
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