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Re: [Xen-devel] USB virt status --- Help please!!!




On 14 Nov 2005, at 17:30, Stephen C. Tweedie wrote:

Having swiotlb the default would also have dealt with the network DMA
problem we had recently, with pci_map_single() refusing to work over
page boundaries.

That got fixed that by adding an arch-specific __alloc_skb which avoided
crossing page boundaries by disabling CONFIG_DEBUG_SLAB for the skb
caches.  But that fix is also something that I doubt maintainers will
allow to go upstream.  I wonder if we'll find enough such special cases
that we really want to have a swiotlb available, just in case, at all
times?

swiotlb performance is pretty poor since it involves memcpy. The alloc_skb fix was pretty clean, if we're allowed an arch hook for alloc_skb. We didn;t need to hack the slab allocator itself.

 -- Keir


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