On Sun, 2013-07-28 at 16:20 -0700, Eric Dumazet wrote: > On Sun, 2013-07-28 at 16:01 -0700, Eric Dumazet wrote: > > On Sun, 2013-07-28 at 21:22 +0100, Ben Hutchings wrote: > > > > > > > > Since we know lengths > 4K work, perhaps it would be worth testing with > > > the fragment cache size reduced to 16K? The driver would never > > > previously have used RX buffers crossing 16K boundaries, except if SLOB > > > was used (and that's an unlikely combination). > > > > Sure, please note the following maths : > > > > NET_SKB_PAD + 1536 + sizeof(struct skb_shared_info) = 1920 > > > > 16384/1920 = 8 > > > > 32768/1920 = 17 > > > > I don't think atl1c is used in any critical host (given it doesn't even > > provide RX checksums and GRO ...), so I will provide a patch doing mere > > page allocations. > > > > Oh well, look at code around line 2530 > > * The atl1c chip can DMA to 64-bit addresses, but it uses a single > * shared register for the high 32 bits, so only a single, aligned, > * 4 GB physical address range can be used at a time. > * > * Supporting 64-bit DMA on this hardware is more trouble than it's > * worth. It is far easier to limit to 32-bit DMA than update > * various kernel subsystems to support the mechanics required by a > * fixed-high-32-bit system. > */ > if ((pci_set_dma_mask(pdev, DMA_BIT_MASK(32)) != 0) || > (pci_set_consistent_dma_mask(pdev, DMA_BIT_MASK(32)) != 0)) { > dev_err(&pdev->dev, "No usable DMA configuration,aborting\n"); > goto err_dma; > } > > It looks like we have a winner ! > > This $@!? really needs DMA32 allocations. [...] Just like many older PCI/PCIe devices. So what? pci_map_single() takes care of that, just so long as the driver sets the DMA mask correctly. In fact, PCI devices have a 32-bit DMA mask by default. Ben. -- Ben Hutchings, Staff Engineer, Solarflare Not speaking for my employer; that's the marketing department's job. They asked us to note that Solarflare product names are trademarked. -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html