Messages in this thread | | | Date | Fri, 21 Nov 2008 18:19:52 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH 03/10] x86: add initialization code for DMA-API debugging |
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* Joerg Roedel <joerg.roedel@amd.com> wrote:
> On Fri, Nov 21, 2008 at 05:56:28PM +0100, Ingo Molnar wrote: > > > + return (entry->dev_addr >> HASH_FN_SHIFT) & HASH_FN_MASK; > > > +} > > > + > > > +static struct dma_debug_entry *dma_entry_alloc(void) > > > +{ > > > + gfp_t gfp = GFP_KERNEL | __GFP_ZERO; > > > + > > > + if (in_atomic()) > > > + gfp |= GFP_ATOMIC; > > > + > > > + return kmem_cache_alloc(dma_entry_cache, gfp); > > > > hm. that slab allocation in the middle of DMA mapping ops makes me a > > bit nervous. the DMA mapping ops are generally rather atomic. > > > > and in_atomic() check there is a bug on !PREEMPT kernels, so it wont > > fly. > > I am not sure I understand this correctly. You say the check for > in_atomic() will break on !PREEMPT kernels?
Correct. There is no check to be able to tell whether we can schedule or not. I.e. on !PREEMPT your patches will crash and burn.
> > We dont have a gfp flag passed in as all the DMA mapping APIs > > really expect all allocations having been done in advance already. > > Hmm, I can change the code to pre-allocate a certain (configurable?) > number of these entries and disble the checking if we run out of it.
yeah, that's a good approach too - that's what lockdep does. Perhaps make the max entries nr a Kconfig entity - so it can be tuned up/down depending on what type of iommu scheme is enabled.
Ingo
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