The following reply was made to PR usb/156596; it has been noted by GNATS.
From: Colin Percival <cperc...@freebsd.org>
To: bug-follo...@freebsd.org, Hans Petter Selasky <hsela...@freebsd.org>
Cc:
Subject: Re: usb/156596: [ehci] Extremely high interrupt rate on ehci/uhci
IRQ16 80% cpu utilization on CPU0
Date: Fri, 08 Jul 2011 17:26:37 -0700
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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 hack.
--
Colin Percival
Security Officer, FreeBSD | freebsd.org | The power to serve
Founder / author, Tarsnap | tarsnap.com | Online backups for the truly paranoid
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--- sys/dev/usb/controller/ehci.c.orig 2011-07-08 16:48:10.000000000 +0000
+++ sys/dev/usb/controller/ehci.c 2011-07-08 16:49:18.000000000 +0000
@@ -1177,7 +1177,9 @@
sqh->prev = 0;
usb_pc_cpu_flush(sqh->page_cache);
- }
+ } else if (last == sqh)
+ last = NULL;
+
return (last);
}
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