On Tue, Feb 05, 2013 at 05:06:28PM +0000, Russell King - ARM Linux wrote: > On Tue, Feb 05, 2013 at 04:47:05PM +0000, Mark Brown wrote: > > On Tue, Feb 05, 2013 at 05:21:48PM +0100, Linus Walleij wrote:
> > > For IRQ mode, use the completion callback to push each cookie > > > to NAPI, and thus let the IRQ drive the traffic. > > The whole purpose of NAPI is to avoid taking interrupts for completion > > of transfers. Anything that generates interrupts when NAPI is in > > polling mode is defeating the point. > Yes, but you're missing one very important point. If your DMA engine > is decoupled from the network device, and the DMA engine relies upon > interrupts to queue further transfers to move data into RAM, then you > have two options: > 1. Receive these interrupts so you can update the DMA engine for > further data transfer. > 2. Don't receive these interrupts, and cause the network device to > error out with a FIFO overrun because its DMA requests have not > been serviced. (which may raise an interrupt.) There's still the third option of just implementing a non-NAPI driver, though I guess we've now built so much infrastructure on top of NAPI that it's still useful to pretend we can disable interrupts.
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