linux-kernel - Re: [PATCH] Option to disable AMD C1E (allows dynticks to work)

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Date:	Sat, 29 Dec 2007 09:43:29 -0500
From:	"David P. Reed" <dpreed@...d.com>
To:	Islam Amer <pharon@...il.com>,
	Richard Harman <richard@...hardharman.com>,
	Eduard-Gabriel Munteanu <eduard.munteanu@...ux360.ro>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Rene Herman <rene.herman@...access.nl>
Subject: Re: [PATCH] Option to disable AMD C1E (allows dynticks to work)

Islam Amer wrote:
> Hello.
> I was interested in getting dynticks to work on my compaq presario v6000
> to help with the 1 hour thirty minutes battery time, but after this
> discussion I lost interest.
>
> I too had the early boot time hang, and found it was udev triggering the
> bug.
>   
This early boot time hang is *almost certainly* due to the in/out port 
80 bug, which I discovered a few weeks ago, which affects hwclock and 
other I/O device drivers on a number of HP/Compaq machines in exactly 
this way.  The proper fix for this bug is in dispute, and will probably 
not occur in the 2.6.24 release because it touches code in many, many 
drivers.  The simplest way to test if you have a problem of this sort is 
to try this shell line as root, after you boot successfully.  If your 
machine hangs hard,  you have a problem that really looks like the port 
80 problem.

for ((i = 0; i < 1000; i = i + 1)); do cat /dev/nvram > /dev/null; done

I have also attached a c program that only touches port 80.  Compile it 
for 32-bit mode (see comment), run it as root, and after two or three 
runs, it will hang a system that has the port 80 bug.

If you then run:

dmidecode -s baseboard-manufacturer
dmidecode -s baseboard-product-name

are the values you should plug into the .matches field in the 
dmi_system_id struct in the attached patch. It would be great if you 
could do that, test, and post back with those values so they can be 
accumulated.  HP/Compaq machines with quanta m/b's are very popular, and 
very common - so at least a quirk patch for all the broken models would 
be worth doing in 2.6.25 or downstream in the distros.  The right 
patches will probably take a long time - there is a dispute as to what 
the semantics of port 80 writes even mean among the core kernel 
developers, because the hack is lost in the dim dark days of history, 
and safe resolution will take time

There is also a C1E issue with the BIOS in my machine (an HP Pavilion 
dv9000z).  I don't know if it is a bug, yet, but that's a different 
problem - associated with dynticks, perhaps.  I have to say that 
researching the AMD Kernel/BIOS docs on C1E (a very new feature in the 
last year on AMD) leaves me puzzled as to whether the dynticks problem 
exists on my machine at all, but the patch for it turns off dynticks!

> Changing the /etc/init.d/udev script so that the line containing
>
> /sbin/udevtrigger
>
> to
>
> /sbin/udevtrigger --subsystem-nomatch="*misc*"
>
> seemed to fix things.
>
> the hang is triggered specifically by 
>
> echo add > /sys/class/misc/rtc/uevent
> after inserting rtc.ko
>
> Also using hwclock to set the rtc , will cause a hard hang, if you are
> using 64bit linux. Disable the init scripts that set the time, or use
> the 32bit binary, as suggested here : 
>
> http://www.mail-archive.com/opensuse@opensuse.org/msg41964.html
>
> I hope this helps. But your hardware is slightly different though.
>   

View attachment "dmi-port80-minimal-bootparam.diff" of type "text/x-patch" (10708 bytes)

View attachment "port80.c" of type "text/x-csrc" (1144 bytes)