Re: is CONFIG_PACKET_MMAP always a win?
Mike Fedyk (firstname.lastname@example.org)
Fri, 22 Feb 2002 13:44:08 -0800
On Fri, Feb 22, 2002 at 07:57:33PM +0000, Alan Cox wrote:
> > > You can process them in the ring buffer. If you can't keep up then you
> > > are screwed any way you look at it 8)
> > That still doesn't avoid copying: af_packet copies the whole packet (if
> > you want the whole packet) from the original skbuff to the ring buffer.
> I'd make a handwaved claim that the first copy of the packet from a DMA
> receiving source is free. Its certainly pretty close to free because the
> overhead of sucking it into L1 cache will dominate and you need to do that
Doesn't DMA access system memory directly and leave processor caches alone?
If so, then the fewer copies that have to pollute the L1/2 caches the better.
Even if it does for UP, I'd immagine that it doesn't for SMP...
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