linux-kernel - Re: [PATCH v6 2/2] PCI: Try best to allocate pref mmio 64bit above 4g

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Message-ID: <CAE9FiQU88EO=e+CR7RKnZ6r7ofSwi9J1QisnrnDyDz6Qh367YQ@mail.gmail.com>
Date:	Sun, 22 Dec 2013 17:14:12 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	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 v6 2/2] PCI: Try best to allocate pref mmio 64bit above 4g

On Sun, Dec 22, 2013 at 4:00 PM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
> On Thu, Dec 19, 2013 at 1:44 PM, Yinghai Lu <yinghai@...nel.org> wrote:
>
> Let me see if I can figure out what you're trying to do here.  Please
> correct me if I'm wrong:
>
>> When one of children resources does not support MEM_64, MEM_64 for
>> bridge get reset, so pull down whole pref resource on the bridge under 4G.
>
> When we allocate space for a bridge's prefetchable window, we
> currently look at the devices behind the bridge and put the window
> below 4GB if any of those children has a 32-bit prefetchable BAR.
>
> This maximizes the use of prefetch, at the cost of using more 32-bit
> address space.

yes. and we have problem when we have 8 sockets or 32 sockets system,
will have limit 32bit space.
but we have enough above 4G 64bit mmio for prefetchable.

>
>> If the bridge support pref mem 64, will only allocate that with pref mem64 to
>> children that support it.
>> For children resources if they only support pref mem 32, will allocate them
>> from non pref mem instead.
>
> You are changing this so that we will always try to put a bridge's
> 64-bit prefetchable window above 4GB, regardless of what devices are
> behind the bridge.  If a device behind the bridge has a 32-bit
> prefetchable BAR, we will place that BAR in the bridge's 32-bit
> non-prefetchable window.

Yes. so we can keep IORESOURCE_MEM64 in the flags for PREF.

>
> This minimizes the use of the 32-bit address space, at the cost of not
> being able to use prefetch as much.
>
>> If the bridge only support 32bit pref mmio, will still have all children pref
>> mmio under that.
>
> Obviously, if a bridge has a prefetchable window that's only 32 bits,
> 64-bit prefetchable BARs behind the bridge will have to be in that
> 32-bit prefetchable window or the 32-bit non-prefetchable window.  And
> if the bridge has no prefetchable window at all, every memory BAR
> behind the bridge will have to be in the 32-bit non-prefetchable
> window.

Yes.

>
> I'll look at the actual patch later; I just want to make sure I
> understand your intent first.

Thanks

Yinghai
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