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SubjectRe: [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:

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.

- Tear

Choose the right car based on your needs. Check out Yahoo! Autos new Car Finder tool. linux- 2007-06-02 14:17:10.000000000 +0000
+++ linux- 2007-06-02 22:24:44.000000000 +0000
@@ -35,6 +35,7 @@
#include <linux/msi.h>
#include <linux/htirq.h>
#include <linux/freezer.h>
+#include <linux/dmi.h>

#include <asm/io.h>
#include <asm/smp.h>
@@ -44,6 +45,7 @@
#include <asm/nmi.h>
#include <asm/msidef.h>
#include <asm/hypertransport.h>
+#include <asm/acpi.h>

#include <mach_apic.h>
#include <mach_apicdef.h>
@@ -98,6 +100,33 @@
unsigned int data;

+static int __init disable_gx240_ioapic(struct dmi_system_id *d)
+ /* Disable IO-APIC only if ACPI is disabled */
+ if (acpi_disabled) {
+ printk(KERN_WARNING "%s detected... Disabling IO-APIC\n", d->ident);
+ skip_ioapic_setup = 1;
+ }
+ return(0);
+static struct dmi_system_id __initdata ioapic_blacklist_dmi_table[] = {
+ {
+ .callback = disable_gx240_ioapic,
+ .ident = "Dell OptiPlex GX240",
+ .matches = {
+ DMI_MATCH(DMI_SYS_VENDOR, "Dell Computer Corporation"),
+ },
+ },
+ { }
+void __init check_ioapic_blacklist(void) {
+ printk(KERN_INFO "Checking for IO-APIC blacklisted systems...\n");
+ dmi_check_system(ioapic_blacklist_dmi_table);
static __attribute_const__ struct io_apic __iomem *io_apic_base(int idx)
return (void __iomem *) __fix_to_virt(FIX_IO_APIC_BASE_0 + idx)
--- linux- 2007-06-02 14:17:10.000000000 +0000
+++ linux- 2007-06-02 22:39:46.000000000 +0000
@@ -124,6 +124,7 @@

extern void early_cpu_init(void);
+extern void check_ioapic_blacklist(void);
extern int root_mountflags;

unsigned long saved_videomode;
@@ -642,6 +643,11 @@
+#ifdef CONFIG_X86_IO_APIC
+ check_ioapic_blacklist(); /* This must be after acpi_boot_init */
if (smp_found_config)
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