diff -Napur -X /home/jbarnes/dontdiff linux-2.6.18/arch/x86_64/kernel/entry.S linux-2.6.18-slow/arch/x86_64/kernel/entry.S
--- linux-2.6.18/arch/x86_64/kernel/entry.S	2006-09-19 20:42:06.000000000 -0700
+++ linux-2.6.18-slow/arch/x86_64/kernel/entry.S	2007-03-15 09:39:27.000000000 -0800
@@ -218,6 +218,8 @@ ENTRY(system_call)
 	testl $(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT|_TIF_SECCOMP),threadinfo_flags(%rcx)
 	CFI_REMEMBER_STATE
 	jnz tracesys
+//	jmp syscall_delay_hack
+ret_from_delay:
 	cmpq $__NR_syscall_max,%rax
 	ja badsys
 	movq %r10,%rcx
@@ -289,6 +291,14 @@ sysret_signal:
 badsys:
 	movq $-ENOSYS,RAX-ARGOFFSET(%rsp)
 	jmp ret_from_sys_call
+#if 0
+syscall_delay_hack:	
+	SAVE_REST
+	call syscall_delay
+	LOAD_ARGS ARGOFFSET  /* reload args from stack in case ptrace changed it */
+	RESTORE_REST
+	jmp ret_from_delay
+#endif
 
 	/* Do syscall tracing */
 tracesys:			 
diff -Napur -X /home/jbarnes/dontdiff linux-2.6.18/arch/x86_64/kernel/irq.c linux-2.6.18-slow/arch/x86_64/kernel/irq.c
--- linux-2.6.18/arch/x86_64/kernel/irq.c	2006-09-19 20:42:06.000000000 -0700
+++ linux-2.6.18-slow/arch/x86_64/kernel/irq.c	2007-03-15 09:36:27.000000000 -0800
@@ -108,6 +108,16 @@ skip:
 	return 0;
 }
 
+static int irq_delay;
+
+static int __init irq_delay_hack(char *str)
+{
+	irq_delay = simple_strtol(str, NULL, 0);
+	return 1;
+}
+__setup("irq_delay=", irq_delay_hack);
+
+
 /*
  * do_IRQ handles all normal device IRQ's (the special
  * SMP cross-CPU interrupts have their own specific
@@ -124,6 +134,9 @@ asmlinkage unsigned int do_IRQ(struct pt
 		BUG();
 	}
 
+	/* IRQ delay hack to measure performance hit */
+	ndelay(irq_delay);
+
 	exit_idle();
 	irq_enter();
 #ifdef CONFIG_DEBUG_STACKOVERFLOW