Messages in this thread | | | Date | Tue, 25 Aug 2009 23:18:46 -0600 | From | Robert Hancock <> | Subject | Re: how to get a DMA channel near a process? |
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On 08/25/2009 07:05 AM, Brice Goglin wrote: > Hello, > > I am playing with DMA engine on a Nehalem box with two X58 chipsets > (Supermicro X8DAH). My understanding is that there are 8 DMA channels on > each chipset, so 8 channels near each processor. Unfortunately, my BIOS
Don't think that DMA channel is the term you are looking for, maybe PCI Express lanes? DMA channels are an ancient ISA thing.
> and 2.6.31-rc still wrongly reports the physical location of my devices > (it claims all PCI devices are near the first processor) but I worked > around the problem manually.
Presumably incorrect information in the BIOS tables (SLIT or MADT, maybe?)
> > The offloaded copy performance changes a lot depending on whether the > process memory is allocated near the DMA device. So first I would like > to know if DMA channels are allocated near the requesting > processor/process. Then I guess it's possible to read the cpu mask near
Not sure quite what you are trying to say here. Normally when memory is allocated for DMA use for a specific device I believe the kernel tries to allocate it on the same node that the device is attached to.
> a given chan by following chan->dev.device up to the pci device, right? > But is there any way to request a DMA channel near a specific socket or > NUMA node or cpu mask? > > Thanks, > Brice > >
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