Hi, 2011/10/12 Gilles Chanteperdrix <gilles.chanteperd...@xenomai.org>: > On 10/12/2011 12:12 AM, Alexis Berlemont wrote: >> The methods are not the same at that level: >> - comedi: n * dma_alloc_coherent + a vmap at the end >> - analogy: a big vmalloc + n * page_to_phys(vmalloc_to_page(vaddr) > > I do not know if that makes a difference, but the result of > dma_alloc_coherent is memory physically contiguous, whereas it is not > the case for memory returned by vmalloc
I don't think comedi guys are using dma_alloc_coherent() for contiguity: they are asking for PAGE_SIZE many times; they just want blocks of 4KB (like analogy, I think). . > > dma_alloc_coherent also allows the GFP_DMA32 flag if you want 32 bits > memory. The striking point is that the flags used are GFP_KERNEL | __GFP_COMP not GFP_DMA32... . There might be a bug in Comedi too, which has not occured yet. Have you already used __GFP_COMP (/* Add compound page metadata */)? Many thanks for your help. Alexis. > > -- > Gilles. > _______________________________________________ Xenomai-help mailing list Xenomai-help@gna.org https://mail.gna.org/listinfo/xenomai-help
