Am Montag, 2. Juli 2007 schrieb Alan Stern:
> On Mon, 2 Jul 2007, Oliver Neukum wrote:
>
> > Am Montag, 2. Juli 2007 schrieb Alan Stern:
> > > > As noted above, for full speed devices we could get similar throughput
> > > > with slightly more clever implementation of scatterlist handling. If
> > > > the HCD has good hardware support for queueing, and the system has fair
> > > > IRQ latency, recycling as few as five URBs might give similar throughput
> > > > to the current "URB per element" approach.
> > >
> > > I think we definitely should do this. For high speed the advantages
> > > aren't so great, since the amount of data needed to fill the pipeline
> > > is about the same as the default max transfer size anyway.
> >
> > Doesn't this boil down to using CPU cycles to save memory?
> > Even worse, many of these cycles would be used in interrupt context.
>
> I don't think so. For one thing, we'd be allocating fewer URBs. For
> another, the total number of submissions would be the same; they would
> just be spread out in time instead of all at once.
But the number of interrupts would grow. The ideal number of interrupts
per transfer is 1. If you can avoid using more by using a bit more
memory, is a wińning strategy.
> Actually, the best way to approach this would be to relax the guarantee
> that completion routines are called with interrupts disabled. There's
> no real reason for that guarantee; it's just an historical remnant.
It speeds up execution in real interrupts, which is good.
Completion handlers might be called in a bottom half, but this
is a rather intrusive change.
Regards
Oliver
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