Messages in this thread | | | Date | Sun, 03 Jun 2001 09:00:24 -0700 | From | David Brownell <> | Subject | Re: [linux-usb-devel] *BAD* impact of usb on PCI performance |
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> From: "Georg Acher" <acher@in.tum.de> > On Sat, Jun 02, 2001 at 01:22:00PM +0200, Pavel Machek wrote: > > > > With Acher's uhci, even ifconfig up of usb-to-usb networking device > > [plusb handled by generic usb-to-usb driver; see -ac series]. > > does 50% slowdown. When fsbr is being used, systems slows down by 350% > > Hm, the 50% make me curious... have to look what's happening...
For PL-2301/2302 devices, "ifconfig up" is mostly just posting a bulk read. True with both "usbnet" and its (now obsolete) predecessor drivers "plusb" and (for different devices) "net1080".
Laplink-style cables can often support another mode (poll via USB "interrupts", and then issue reads only when data is available) but not every device can work that way (like, I seem to recall, an iPaq PDA). And that'd increase the latency per packet by a couple milliseconds, even when it's possible.
> > (running more than 4 times slower than normally. Ouch). > > Blame Intel. Either low latency or low PCI usage, you can choose...
This problem is UHCI-specific, not USB-generic, yes? Doesn't happen with OHCI?
- Dave
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