Re: Long max latencies on Wandbaord / Freescale i.MX6

[Matthias Meier <matthias.j.meier@gmx.net>]

PROVE_LOCKING is not so bad I thought

finally I guess my latency problem is caused by a spurious interrupt on 
a unused mmc slot causing heavy load when using PROVE_LOCKING ...


Here a little more in detail what I did:

Disabling CONFIG_PROVE_LOCKING together with a lot other debug options 
as Thomas proposed indeed gave max latencies in the range of 100us - at 
least most of the time...

After adding besides 'hackbench' additional heavy network load via the 
on-board WiFi interface, the max latency raised further and finally I 
the kernel fired a backtrace which ended in a "Disabling IRQ #284"

/proc/interrupts indeed shows a hugh amout of interrupts on mmc1 
although I don't use mmc1 at all (the Wandboard boots via mmc0)

(possible a pullup config is missing at the mmc interfaces?)

After reboot I tried to stop the spurious interrupts by inserting a 
sd-card on mmc1 but this does not work - still high interrupts.

Now I'm trying to disable mmc1 and mmc2 completely which is not as easy 
as I thought: via sysfs it seems not to be possible and via DT I think I 
would have to modify all imx6* DTS files of all imx6 boards - otherwise 
the dtbs does not compile...


Is there a simple solution to disable either a single interrupt or a 
individual mmc interface from userspace?

Thanks,
	Matthias