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

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Date:	Sat, 2 Jun 2007 07:10:58 -0700 (PDT)
From:	Tear <tarrqt@...oo.com>
To:	mingo@...hat.com
Cc:	akpm@...ux-foundation.org, torvalds@...ux-foundation.org,
	linux-kernel@...r.kernel.org
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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View attachment "io_apic-patch.diff" of type "text/x-patch" (1909 bytes)