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Subject[RFC][PATCH] IO-APIC blacklist
Hi,

I own a Dell OptiPlex GX240 which, when ACPI is disabled
but IO-APIC is enabled, shows very slow USB performance.
I thought that this could be related to IO-APIC and
tried to boot with "noapic" appended to the kernel
command line. This way the USB transfer speed returned
to normal values.

To make sure that noone else encounters a similar problem,
I have written a patch which includes an IO-APIC blacklist
and disables IO-APIC according to the blacklist.

I would like this patch to be merged into the main
tree. If there is any revision/correction that needs to
be done on the patch, please let me know.

I would appreciate any comments.

Thank you for your attention.

Regards,
- Tear

Note: The patch is appended and attached (in case
Yahoo wraps some lines.)

diff -u -r linux-2.6.21.3.orig/arch/i386/kernel/io_apic.c
linux-2.6.21.3/arch/i386/kernel/io_apic.c
--- linux-2.6.21.3.orig/arch/i386/kernel/io_apic.c 2007-06-01 19:01:35.000000000 +0000
+++ linux-2.6.21.3/arch/i386/kernel/io_apic.c 2007-06-01 21:00:46.000000000 +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>
@@ -98,6 +99,30 @@
unsigned int data;
};

+static int __init disable_blacklisted_ioapic(struct dmi_system_id *d)
+{
+ 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_blacklisted_ioapic,
+ .ident = "Dell OptiPlex GX240",
+ .matches = {
+ DMI_MATCH(DMI_SYS_VENDOR, "Dell Computer Corporation"),
+ DMI_MATCH(DMI_PRODUCT_NAME, "OptiPlex GX240"),
+ },
+ },
+ { }
+};
+
+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)
diff -u -r linux-2.6.21.3.orig/arch/i386/kernel/setup.c linux-2.6.21.3/arch/i386/kernel/setup.c
--- linux-2.6.21.3.orig/arch/i386/kernel/setup.c 2007-06-01 19:01:35.000000000 +0000
+++ linux-2.6.21.3/arch/i386/kernel/setup.c 2007-06-01 21:04:01.000000000 +0000
@@ -124,6 +124,7 @@
#endif

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

unsigned long saved_videomode;
@@ -616,6 +617,11 @@
#ifdef CONFIG_X86_GENERICARCH
generic_apic_probe();
#endif
+
+#ifdef CONFIG_X86_IO_APIC
+ check_ioapic_blacklist();
+#endif
+
if (efi_enabled)
efi_map_memmap();







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--- linux-2.6.21.3.orig/arch/i386/kernel/io_apic.c 2007-06-01 19:01:35.000000000 +0000
+++ linux-2.6.21.3/arch/i386/kernel/io_apic.c 2007-06-01 21:00:46.000000000 +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>
@@ -98,6 +99,30 @@
unsigned int data;
};

+static int __init disable_blacklisted_ioapic(struct dmi_system_id *d)
+{
+ 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_blacklisted_ioapic,
+ .ident = "Dell OptiPlex GX240",
+ .matches = {
+ DMI_MATCH(DMI_SYS_VENDOR, "Dell Computer Corporation"),
+ DMI_MATCH(DMI_PRODUCT_NAME, "OptiPlex GX240"),
+ },
+ },
+ { }
+};
+
+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)
diff -u -r linux-2.6.21.3.orig/arch/i386/kernel/setup.c linux-2.6.21.3/arch/i386/kernel/setup.c
--- linux-2.6.21.3.orig/arch/i386/kernel/setup.c 2007-06-01 19:01:35.000000000 +0000
+++ linux-2.6.21.3/arch/i386/kernel/setup.c 2007-06-01 21:04:01.000000000 +0000
@@ -124,6 +124,7 @@
#endif

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

unsigned long saved_videomode;
@@ -616,6 +617,11 @@
#ifdef CONFIG_X86_GENERICARCH
generic_apic_probe();
#endif
+
+#ifdef CONFIG_X86_IO_APIC
+ check_ioapic_blacklist();
+#endif
+
if (efi_enabled)
efi_map_memmap();
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