iosched: effect of streaming write on interactivity

[Andrew Morton]

It peeves me that if a machine is writing heavily, it takes *ages* to get a
login prompt.

Here we start a large streaming write, wait for that to reach steady state
and then see how long it takes to pop up an xterm from the machine under
test with

	time ssh testbox xterm -e true

there is quite a lot of variability here.

2.4.21-4:	62 seconds
2.5.61+hacks:	14 seconds
2.5.61+CFQ:	11 seconds
2.5.61+AS:	12 seconds