On Sunday 01 May 2005 1:37 pm, Eric Blossom wrote: > > I think the biggest benefit would be in giving us potentially lower > latency. Right now, our throughput bottleneck is in the firmware in > the FX2. We currently get 32MB/sec. We know that at least for > unidirectional apps (might not apply to us) 40MB/sec is possible with > the FX2.
But not necessarily all EHCI controllers, or all systems. I've benched almost 40 MB/sec on some systems; others have a hard time topping 12 MB/sec, seemingly due to PCI or southbridge problems. And one system that's previously given me 32 MB/sec seems to have taken about 6 MB/sec away from me, I'm not sure where it's gone. :( > With regard to the cost of the user to kernel copy, I suggest making > measurements. Last time I checked, the driver was only taking up on > the order of 5% of the CPU. Good point. A while back I remember doing some stuff that streamed 24 MByte/sec to userspace, single copy on an Athlon. That ran something like 10% of that CPU, which was pretty slow by today's standards. It was using "high bandwidth isochronous transfers", which aren't the most CPU-efficient mode to work with. (Each 3KB packet was an indivdiual AIO request.) - Dave ------------------------------------------------------- This SF.Net email is sponsored by: NEC IT Guy Games. Get your fingers limbered up and give it your best shot. 4 great events, 4 opportunities to win big! Highest score wins.NEC IT Guy Games. Play to win an NEC 61 plasma display. Visit http://www.necitguy.com/?r=20 _______________________________________________ linux-usb-devel@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
