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SubjectRe: Today Linus redesigns the networking driver interface (was Re: tulip driver in ...)
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> That sounds like we're really spending most of our time actually handling
> the physical interrupt. Is that right? That implies we don't even get to
> the networking layer, we're just too slow getting the packet off the card.
> And that's scary.

Take a non DMA into packet driver. You receive packets at 10Mbytes/second.
Each packet has to be copied into a buffer. Because we are handling 128
byte packets we are copying. Each packet is in main memory and has
invalidated L1 and L2 caches from the DMA to the ring buffer.

You have 80,000 packets per second to field for 100Mbit in 128 byte frames
Which I make 12uS an interrupt including hardware latencies.

Gigabit you can multiply that by a bit more and thank the card designers
its not by ten.

So you have to have flow control at the physical interrupt level, and since
you have to switch packets at the physical IRQ level to make anything work
at those speeds its all part of the same thing.

Alan



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