On Thu, Sep 17, 2015 at 03:02:51PM -0400, Konrad Rzeszutek Wilk wrote: > On Thu, Sep 17, 2015 at 02:22:38PM -0400, jgli...@redhat.com wrote: > > From: Jérôme Glisse <jgli...@redhat.com> > > > > The swiotlb dma backend is not appropriate for some devices like > > GPU where bounce buffer or slow dma page allocations is just not > > acceptable. With that helper device drivers can opt-out from the > > swiotlb and just do sane things without wasting CPU cycles inside > > the swiotlb code. > > What if SWIOTLB is the only one available?
On x86 no_mmu is always available and we assume that device driver that would use this knows that their device can access all memory with no restriction or at very least use DMA32 gfp flag. > And what can't the devices use the TTM DMA backend which sets up > buffers which don't need bounce buffer or slow dma page allocations? We want to get rid of this TTM code path for radeon and likely nouveau. This is the motivation for that patch. Benchmark shows that the TTM DMA backend is much much much slower (20% on some benchmark) that the regular page allocation and going through no_mmu. So this is all about allowing to directly allocate page through regular kernel page alloc code and not through specialize dma allocator. Cheers, Jérôme -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
