linux-kernel - Re: [PATCH] TTM DMA pool v2.2 or [GIT PULL] (stable/ttm.dma

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Date:	Fri, 4 Nov 2011 15:41:03 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Jerome Glisse <j.glisse@...il.com>
Cc:	linux-kernel@...r.kernel.org, thellstrom@...are.com,
	thomas@...pmail.org, airlied@...hat.com, jglisse@...hat.com,
	bskeggs@...hat.com, xen-devel@...ts.xensource.com
Subject: Re: [PATCH] TTM DMA pool v2.2 or [GIT PULL]
 (stable/ttm.dma_pool.v2.3) for 3.3

On Fri, Nov 04, 2011 at 03:24:51PM -0400, Jerome Glisse wrote:
> On Fri, Nov 04, 2011 at 02:44:53PM -0400, Konrad Rzeszutek Wilk wrote:
> > > > git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen.git stable/ttm.dma_pool.v2.3
> > > > 
> > > 
> > > On what hw did you tested ? With and without xen ? Here radeon
> > 
> > On AMD and Intel. And with both Nvidia and Radeon cards.
> > 64-bit cards (I have a patch where I forced the 64-bit card to use
> > the TTM DMA pool code to test) and 32-bit cards (ATI ES1000)
> > 
> > On baremetal and Xen. Um, Fedora Core 16 as distro.
> > 
> > Oh, and I also tried PPC (Power Mac 4) but could not get it to boot
> > the 3.1 kernel. Something with the LILO grub loader did not work.
> > 
> > > that doesn't need dma32 doesn't work when forcing swiotlb which
> > > kind of expected i guess. Should we expose if swiotlb is enabled
> > 
> > You did 'swiotlb=force' ?
> > > forced so we use dma pool in such case ?
> 
> Issue is that when booted without force swiotlb_nr_tlb still return
> positive thus we endup using the dma pool path.

Did " Using software bounce buffering for IO (SWIOTLB)" or "software IO TLB at"
show up in the dmesg output? You might have to run it with 'debug loglevel=8'?
Presumarily yes, since the code "swiotlb: Expose.." sets
  io_tlb_nslabs = 0

if there is no need for it. And since io_tlb_nslabs is set, then the code
did start.

Some AMD boxes with the AMD-Vi chipset enable the SWIOTLB b/c not all of
the PCI devices are on the IOMMU chipset path. The Intel VT-d does the same
thing.

Hmm, I think the reason for those devices to turn SWIOTLB on is that they
are not comfortable handling 32-bit devices, and the TTM DMA pool code would
only turn itself on when the radeon|nouveau was 32-bit _and_ SWIOTLB was enabled.

.. Testing the patches you posted on my AMD box.
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