linux-kernel - Re: [RFC][PATCH] IO-APIC blacklist

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Date:	Sat, 2 Jun 2007 16:48:05 -0700 (PDT)
From:	Tear <tarrqt@...oo.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Len Brown <lenb@...nel.org>, mingo@...hat.com,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] IO-APIC blacklist

Linus Torvalds wrote:
> On Sat, 2 Jun 2007, Tear wrote:
> > >
> > > Wouldn't this also disable the IOAPIC in the (working) ACPI+IOAPIC case?
> >
> > Yes, it would. However, I wanted to make my addition
> > to the kernel generic so that other people with
> > problematic IO-APIC implementations can blacklist
> > their systems without checking whether ACPI is enabled
> > or not.
> 
> But that's just wrong. First off, all distro kernels come with ACPI on, so
> the thing you're fixing is really just for somebody who compiles his own
> kernel in a particular (and unusual/strange) configuration, and you're
> making it _worse_ for everybody else.

Mr. Torvalds,

The patch scans the DMI for "Dell OptiPlex GX240"
and disables IO-APIC only if such a system is detected.
It does not disable IO-APIC for other people.

In addition, Dell OptiPlex GX240 is (at least currently)
in the ACPI blacklist. So with a regular distro, one
gets IO-APIC and acpi=ht which causes USB transfers
to be very slow. 

I have made an attempt to get Dell OptiPlex GX240
out of the ACPI blacklist. Please see:
http://marc.info/?t=117897881900001&r=1&w=2

Nevertheless, I am willing to modify the patch
to make IO-APIC work when ACPI is enabled. A
quick search pointed me to the variable named
"acpi_disabled". I can use this variable to
detect whether ACPI is enabled and disable
IO-APIC if it is not. Please see the
attached patch for such an implementation.

> And you're blacklisting it without even understaning _what_ is wrong. I
> really think we should figure that part out first,

I willing to put effort into figuring out what
is wrong. Please let me know if there is anything
I can do to further our information about this
problem. As I said before, I would be glad to
send to you the diff between any of the four
cases I mentioned in my previous e-mail to you.

Were you able to take a look at the dmesg
outputs in my previous e-mail?

Thank you for your attention.

Regards,
- Tear

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View attachment "io_apic-patch2.diff" of type "text/x-patch" (2034 bytes)