Subject: Re: Warning to USB users
To: Lennart Augustsson <>
From: Jason R Thorpe <>
List: current-users
Date: 04/13/2001 10:57:43
On Fri, Apr 13, 2001 at 07:51:30PM +0200, Lennart Augustsson wrote:

 > In a recent change Jason Thorpe turned on an option in the USB drivers
 > that uses soft interrupts.  If a port does not have generic soft interrupts (a
 > prime example is i386) it instead uses a callout.  In the latter case the
 > interrupt latency increases greatly.  For most USB devices this has no
 > consequence, but if you are using, e.g., Ethernet adapters, the performance
 > will be pretty bad (on my machine it went from 700 KB/s to 140 KB/s).
 > If this worries you, just change sys/dev/usb/usb_port.h and comment
 > out the define of USB_USE_SOFTINTR.

Unfortunately, SOFTINTR is going to be required due to another change
I'm going to make today.

I'll see about cooking up a generic soft interrupts implementation
for i386 today/tomorrow (I don't think I can wait for Bill Sommerfeld's
new MP-safe interrupt code to get finished).

        -- Jason R. Thorpe <>