Profiling timing shows that we can do interrupt checks with cost:

* about 2.0 secs per 1 billion checks if the counter is kept in memory
* about 0.5 secs per 1 billion checks if the counter is kept in register.

lab/prof/Makefile

@@ -1,6 +1,4 @@
 
-main: main.c
+main: main.c int.s
-	gcc -m64 -O3 -Wall main.c -o main
+	gcc -Wall main.c int.s -o main
 
-main.s: main.c
-	gcc -m64 -O3 -Wall -fomit-frame-pointer -fno-PIC -S main.c

lab/prof/int.s

@@ -0,0 +1,34 @@
+
+.globl _interrupt_mem
+_interrupt_mem:
+  movl 4(%esp), %eax
+L_loop1:
+  subl $1, 0(%eax);
+  jz L_int1
+  jmp L_loop1
+L_int1:
+  ret
+
+.globl _interrupt_reg
+_interrupt_reg:
+  movl 4(%esp), %eax
+L_loop2:
+  subl $1, %eax;
+  jz L_int2
+  subl $1, %eax;
+  jz L_int2
+  subl $1, %eax;
+  jz L_int2
+  subl $1, %eax;
+  jz L_int2
+  subl $1, %eax;
+  jz L_int2
+  subl $1, %eax;
+  jz L_int2
+  subl $1, %eax;
+  jz L_int2
+  jmp L_loop2
+L_int2:
+  ret
+
+

lab/prof/main.c

@@ -1,14 +1,31 @@
+
 #include <stdio.h>
-
-long long foo(long long int x){
-  return x+1;
-}
-
 #include <stdlib.h>
-int main(int argc, char** argv){
+#include <string.h>
-  fprintf(stderr, "sizeof(long long int)=%ld\n", 
+
-      sizeof(long long int));
+typedef struct pcb{
-  long long int x = 57;
+  int counter;
-  x = foo(x);
+} pcb;
+
+extern void interrupt_mem(pcb*);
+extern void interrupt_reg(int);
+
+void usage(char* name){
+  fprintf(stderr, "Usage: %s [mem|reg]\n", name);
   exit(-1);
 }
+
+int main(int argc, char** argv){
+  int most_positive_number = 0x7FFFFFFF;
+  if(argc != 2) usage(argv[0]);
+  if(strcmp(argv[1], "reg") == 0){
+    interrupt_reg(most_positive_number);
+  } else if(strcmp(argv[1], "mem") == 0){
+    pcb x;
+    x.counter = most_positive_number;
+    interrupt_mem(&x);
+  } else {
+    usage(argv[0]);
+  }
+  return 0;
+}

lab/prof/main.s

@@ -1,77 +0,0 @@
-	.text
-.globl _foo
-_foo:
-LFB3:
-	leaq	1(%rdi), %rax
-	ret
-LFE3:
-	.cstring
-LC0:
-	.ascii "sizeof(long long int)=%ld\12\0"
-	.text
-.globl _main
-_main:
-LFB20:
-	subq	$8, %rsp
-LCFI0:
-	movl	$8, %edx
-	leaq	LC0(%rip), %rsi
-	movq	___stderrp@GOTPCREL(%rip), %rax
-	movq	(%rax), %rdi
-	xorl	%eax, %eax
-	call	_fprintf
-	movl	$-1, %edi
-	call	_exit
-LFE20:
-	.section __TEXT,__eh_frame,coalesced,no_toc+strip_static_syms+live_support
-EH_frame1:
-	.set L$set$0,LECIE1-LSCIE1
-	.long L$set$0
-LSCIE1:
-	.long	0x0
-	.byte	0x1
-	.ascii "zR\0"
-	.byte	0x1
-	.byte	0x78
-	.byte	0x10
-	.byte	0x1
-	.byte	0x10
-	.byte	0xc
-	.byte	0x7
-	.byte	0x8
-	.byte	0x90
-	.byte	0x1
-	.align 3
-LECIE1:
-	.globl _foo.eh
-_foo.eh:
-LSFDE1:
-	.set L$set$1,LEFDE1-LASFDE1
-	.long L$set$1
-LASFDE1:
-	.long	LASFDE1-EH_frame1
-	.quad	LFB3-.
-	.set L$set$2,LFE3-LFB3
-	.quad L$set$2
-	.byte	0x0
-	.align 3
-LEFDE1:
-	.globl _main.eh
-_main.eh:
-LSFDE3:
-	.set L$set$3,LEFDE3-LASFDE3
-	.long L$set$3
-LASFDE3:
-	.long	LASFDE3-EH_frame1
-	.quad	LFB20-.
-	.set L$set$4,LFE20-LFB20
-	.quad L$set$4
-	.byte	0x0
-	.byte	0x4
-	.set L$set$5,LCFI0-LFB20
-	.long L$set$5
-	.byte	0xe
-	.byte	0x10
-	.align 3
-LEFDE3:
-	.subsections_via_symbols

lab/prof/times.txt

@@ -0,0 +1,9 @@
+1 2.157
+2 1.618
+3 1.440
+4 1.350
+5 1.296
+6 1.260
+7 1.232
+
+