Re: e1000 question

[Ihar 'Philips' Filipau]

  Thanks, Mitch!
  That explains everything.

  Went reading pci_alloc_consistent()'s RTFM.
  That is exactly what I was missing in couple of my drivers.

Mitchell Blank Jr wrote:
> Ihar 'Philips' Filipau wrote:
>
> >   Functions e1000_clean_{t,r}x_irq are very similar: both of them are 
> > checking descriptor flag updated by nic.
> >   Host CPU, obviously, to perform this check, will cache descriptor.
> >   If, say e1000_clean_rx_irq() will be called twice in short time 
> > range, I expect that it can miss change of the flag, since old flag may 
> > still sit in host CPU cache.
>
>
> Please see Documentation/DMA-mapping.txt; especially the part starting
> at "There are two types of DMA mappings..."  Ring buffers are allocated
> as "consistent" DMA memory.
>
> For most architectures this will mean that the cache hardware snoops the
> PCI bus and automatically invalidates cache lines as they are written to.
> For architectures that can't do that then Linux will mark those memory
> regions uncacheable.

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