[9fans] usb slowness

[Tristan <9p-st@imu.li>]

for a while now i've known that usb/ether runs slow for me. i thought it
was something to do with the specific situation or hardware, and that,
say, usb/disk would be alright. it isn't. and not just on the olpc. now,
my machines are fairly slow as machines go... but 2.5MB/s reads are a far
cry from 22MB/s (with the olpc on linux).

it turns out that _strayintr is taking up nearly all the time.

cpu% kprof /n/9fat/9cpcpuf /dev/kpdata
total: 24620	in kernel text: 23890	outside kernel text:730
RTZERO f0100000 PGSIZE 4Kb
ms	  %	sym
21840	 91.3	_strayintr
290	  1.2	memmove
290	  1.2	iunlock
180	  0.7	sched
160	  0.6	memset
150	  0.6	sleep
...

my understanding is that _strayintr is glue between the interrupt vector
table and trap. and presumably includes the time spent in trap.

the short review of usbehci.c didn't provide any insight, so i guess i'm
asking, is this expected behavior? and what can i do?

enjoy,
tristan

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