The following reply was made to PR usb/156596; it has been noted by GNATS.
From: Hans Petter Selasky <hsela...@c2i.net>
To: Colin Percival <cperc...@freebsd.org>
Cc: "bug-follo...@freebsd.org" <bug-follo...@freebsd.org>
Subject: Re: usb/156596: [ehci] Extremely high interrupt rate on ehci/uhci
IRQ16 80% cpu utilization on CPU0
Date: Sat, 9 Jul 2011 11:33:40 +0200
On Saturday 09 July 2011 02:26:37 Colin Percival wrote:
> Hi again,
> The attached patch seems to fix the problem while not breaking anything on
> my laptop. It makes handles the case of EHCI_REMOVE_QH(sqh, last) with
> sqh == last and sqh->prev == NULL by setting last = NULL -- the idea being
> that if sqh is the only entry in the queue, we still ought to delete it
> even though it doesn't have a predecessor.
> I have no idea if this is correct, since I don't know the rest of the code
> in this file. Maybe we should also delete the first entry in a queue even
> when it isn't also the last entry; maybe the problem lies somewhere else
> entirely. I'm hoping that someone who knows this code will be able to
> figure out the right fix easily now that I have an apparently-working
The last element should always be there. If it is NULL I would like to see a
backtrace from that. KASSERT(last != NULL) in both add and remove. If you
clear that the USB queue will stop working I believe. Anyway, I think your
clue might give some hints what is wrong. It appears that the EHCI is spinning
on the IDLE queue somehow producing a lot of IRQ's.
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