linux-kernel - PCIe dma-able memory location in physical memory for Intel Nehalem + Tylersburg architecture

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Message-ID: <4CD35CD1F8085945B597F80EEC894213030C20F6@exc01.bk.prodrive.nl>
Date:	Thu, 9 Jul 2009 11:04:59 +0200
From:	"Rob van de Voort" <rob.van.der.voort@...drive.nl>
To:	<linux-kernel@...r.kernel.org>
Subject: PCIe dma-able memory location in physical memory for Intel Nehalem + Tylersburg architecture

Hello,

I have the following question regarding the (re-)allocation of dma-able
memory for a PCIe device. I wish to know on which CPU / Memory
controller the dma-able memory will be allocated. In addition i would
like to know how i can control this allocation process, or how to
reroute it to another CPU / Memory controller.

The system i use contains two Nehalem processors connected via intel QPI
bus. Both processors have 3GB of DDR3 RAM in their memory banks. The
PCIe bus is controlled by a tylersburg io hub which is also connected to
the intel QPI bus

The system runs a 64bit linux kernel. Furthermore a PCIe device which
can only use 32 bit addressing is connected to the PCIe bus. I want to
allocate dma-able memory for this device using a driver, i know how to
do this. For maximal performance i would like to control the allocation
of dma-able memory, in particular the allocation to a certain CPU /
memory controller. The tylersburg IO hub has an influence on this
allocation but can i influence this.

So my questions are:
-1- How can i know were our dma-able memory is allocated in physical
memory?
-2- How can i control / redirect this allocation to a certain memory
controller / CPU?

Thanks for any reply,

Rob van de Voort

P.S  I'd be grateful if people could point me in the direction of
resources I could read. Thus far I have gone over the PCI / DMA
documentation in
the kernel, and a couple of articles on lwn. 
If this is the wrong mailing list for this type of question i hope you
can redirect me to the correct one.

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