Messages in this thread | | | Date | Thu, 09 Nov 2006 01:46:52 -0700 | From | "Jeffrey V. Merkey" <> | Subject | Re: e1000 driver 2.6.18 - how to waste processor cycles |
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Jesse Brandeburg wrote:
> included netdev... > > On 11/8/06, Jeff V. Merkey <jmerkey@soleranetworks.com> wrote: > >> >> Is there a good reason the skb refill routine in e1000_alloc_rx_buffers >> needs to go and touch and remap skb memory >> on already loaded descriptors/ This seems extremely wasteful of >> processor cycles when refilling the ring buffer. >> >> I note that the archtiecture has changed and is recycling buffers from >> the rx_irq routine and when the routine is called >> to refill the ring buffers, a lot of wasteful and needless calls for >> map_skb is occurring. > > > we have to unmap the descriptor (or at least do > pci_dma_sync_single_for_cpu / pci_dma_sync_single_for_device) because > the dma API says we can't be guaranteed the cacheable memory is > consistent until we do one of the afore mentioned pci dma ops.
In the case I am referring to, the memory is already mapped with a previous call, which means it may be getting mapped twice.
Jeff
> > we have to do *something* before we access it. Simplest path is to > unmap it and then recycle/map it. > > If you can show that it is faster to use pci_dma_sync_single_for_cpu > and friends I'd be glad to take a patch. > > Hope this helps, > Jesse > - > To unsubscribe from this list: send the line "unsubscribe > linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ >
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