Anton Blanchard wrote: >> +/* >> + * Set of routunes to get a new receive buffer. Any buffer which >> + * crosses a 4KB boundary must start on a 4KB boundary due to PCIe >> + * wdma restrictions. We also try to align any smaller allocation to >> + * at least a 16 byte boundary for efficiency. We assume the linux >> + * memory allocator works by powers of 2, and will not return memory >> + * smaller than 2KB which crosses a 4KB boundary. If it does, we fall >> + * back to allocating 2x as much space as required. >> + * >> + * We intend to replace large (>4KB) skb allocations by using >> + * pages directly and building a fraglist in the near future. >> + */ >> > > You go to a lot of trouble to align things. One thing on ppc64 is that > we really want to start all DMA writes on a cacheline boundary. We > enforce that in network drivers by making NET_IP_ALIGN = 0 and having > the drivers do: > > skb_reserve(skb, NET_IP_ALIGN); > > It sounds like your small allocations will be only aligned to 16 bytes. >
We didn't get any ppc64 with PCI-E to run Linux so far. What performance drop should we expect with our current code ? > Id suggest using the dma API instead of the pci API. We have seen > machines in the field that have failed large pci_alloc_consistent calls > because it always asks for GFP_ATOMIC memory (it presumes the worst). > The dma API allows you to pass a GFP_ flag in which will have a much > better chance of succeeding when you dont need GFP_ATOMIC memory. > Good idea, thanks, >> +#ifdef CONFIG_MTRR >> + mgp->mtrr = mtrr_add(mgp->iomem_base, mgp->board_span, >> + MTRR_TYPE_WRCOMB, 1); >> +#endif >> > ... > >> + mgp->sram = ioremap(mgp->iomem_base, mgp->board_span); >> > > Not sure how we are meant to specify write through in drivers. Any ideas Ben? > I am not sure what you mean. The only ppc64 with PCI-E that we have seen so far (a G5) couldn't do write combining according to Apple. Thanks, Brice - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
