[PATCH] vm: remove redundant assignment from __pagevec_release_nonlru()
[linux-2.6.git] / init / calibrate.c
1 /* calibrate.c: default delay calibration
2  *
3  * Excised from init/main.c
4  *  Copyright (C) 1991, 1992  Linus Torvalds
5  */
6
7 #include <linux/sched.h>
8 #include <linux/delay.h>
9 #include <linux/init.h>
10
11 #include <asm/timex.h>
12
13 static unsigned long preset_lpj;
14 static int __init lpj_setup(char *str)
15 {
16         preset_lpj = simple_strtoul(str,NULL,0);
17         return 1;
18 }
19
20 __setup("lpj=", lpj_setup);
21
22 #ifdef ARCH_HAS_READ_CURRENT_TIMER
23
24 /* This routine uses the read_current_timer() routine and gets the
25  * loops per jiffy directly, instead of guessing it using delay().
26  * Also, this code tries to handle non-maskable asynchronous events
27  * (like SMIs)
28  */
29 #define DELAY_CALIBRATION_TICKS                 ((HZ < 100) ? 1 : (HZ/100))
30 #define MAX_DIRECT_CALIBRATION_RETRIES          5
31
32 static unsigned long __devinit calibrate_delay_direct(void)
33 {
34         unsigned long pre_start, start, post_start;
35         unsigned long pre_end, end, post_end;
36         unsigned long start_jiffies;
37         unsigned long tsc_rate_min, tsc_rate_max;
38         unsigned long good_tsc_sum = 0;
39         unsigned long good_tsc_count = 0;
40         int i;
41
42         if (read_current_timer(&pre_start) < 0 )
43                 return 0;
44
45         /*
46          * A simple loop like
47          *      while ( jiffies < start_jiffies+1)
48          *              start = read_current_timer();
49          * will not do. As we don't really know whether jiffy switch
50          * happened first or timer_value was read first. And some asynchronous
51          * event can happen between these two events introducing errors in lpj.
52          *
53          * So, we do
54          * 1. pre_start <- When we are sure that jiffy switch hasn't happened
55          * 2. check jiffy switch
56          * 3. start <- timer value before or after jiffy switch
57          * 4. post_start <- When we are sure that jiffy switch has happened
58          *
59          * Note, we don't know anything about order of 2 and 3.
60          * Now, by looking at post_start and pre_start difference, we can
61          * check whether any asynchronous event happened or not
62          */
63
64         for (i = 0; i < MAX_DIRECT_CALIBRATION_RETRIES; i++) {
65                 pre_start = 0;
66                 read_current_timer(&start);
67                 start_jiffies = jiffies;
68                 while (jiffies <= (start_jiffies + 1)) {
69                         pre_start = start;
70                         read_current_timer(&start);
71                 }
72                 read_current_timer(&post_start);
73
74                 pre_end = 0;
75                 end = post_start;
76                 while (jiffies <=
77                        (start_jiffies + 1 + DELAY_CALIBRATION_TICKS)) {
78                         pre_end = end;
79                         read_current_timer(&end);
80                 }
81                 read_current_timer(&post_end);
82
83                 tsc_rate_max = (post_end - pre_start) / DELAY_CALIBRATION_TICKS;
84                 tsc_rate_min = (pre_end - post_start) / DELAY_CALIBRATION_TICKS;
85
86                 /*
87                  * If the upper limit and lower limit of the tsc_rate is
88                  * >= 12.5% apart, redo calibration.
89                  */
90                 if (pre_start != 0 && pre_end != 0 &&
91                     (tsc_rate_max - tsc_rate_min) < (tsc_rate_max >> 3)) {
92                         good_tsc_count++;
93                         good_tsc_sum += tsc_rate_max;
94                 }
95         }
96
97         if (good_tsc_count)
98                 return (good_tsc_sum/good_tsc_count);
99
100         printk(KERN_WARNING "calibrate_delay_direct() failed to get a good "
101                "estimate for loops_per_jiffy.\nProbably due to long platform interrupts. Consider using \"lpj=\" boot option.\n");
102         return 0;
103 }
104 #else
105 static unsigned long __devinit calibrate_delay_direct(void) {return 0;}
106 #endif
107
108 /*
109  * This is the number of bits of precision for the loops_per_jiffy.  Each
110  * bit takes on average 1.5/HZ seconds.  This (like the original) is a little
111  * better than 1%
112  */
113 #define LPS_PREC 8
114
115 void __devinit calibrate_delay(void)
116 {
117         unsigned long ticks, loopbit;
118         int lps_precision = LPS_PREC;
119
120         if (preset_lpj) {
121                 loops_per_jiffy = preset_lpj;
122                 printk("Calibrating delay loop (skipped)... "
123                         "%lu.%02lu BogoMIPS preset\n",
124                         loops_per_jiffy/(500000/HZ),
125                         (loops_per_jiffy/(5000/HZ)) % 100);
126         } else if ((loops_per_jiffy = calibrate_delay_direct()) != 0) {
127                 printk("Calibrating delay using timer specific routine.. ");
128                 printk("%lu.%02lu BogoMIPS (lpj=%lu)\n",
129                         loops_per_jiffy/(500000/HZ),
130                         (loops_per_jiffy/(5000/HZ)) % 100,
131                         loops_per_jiffy);
132         } else {
133                 loops_per_jiffy = (1<<12);
134
135                 printk(KERN_DEBUG "Calibrating delay loop... ");
136                 while ((loops_per_jiffy <<= 1) != 0) {
137                         /* wait for "start of" clock tick */
138                         ticks = jiffies;
139                         while (ticks == jiffies)
140                                 /* nothing */;
141                         /* Go .. */
142                         ticks = jiffies;
143                         __delay(loops_per_jiffy);
144                         ticks = jiffies - ticks;
145                         if (ticks)
146                                 break;
147                 }
148
149                 /*
150                  * Do a binary approximation to get loops_per_jiffy set to
151                  * equal one clock (up to lps_precision bits)
152                  */
153                 loops_per_jiffy >>= 1;
154                 loopbit = loops_per_jiffy;
155                 while (lps_precision-- && (loopbit >>= 1)) {
156                         loops_per_jiffy |= loopbit;
157                         ticks = jiffies;
158                         while (ticks == jiffies)
159                                 /* nothing */;
160                         ticks = jiffies;
161                         __delay(loops_per_jiffy);
162                         if (jiffies != ticks)   /* longer than 1 tick */
163                                 loops_per_jiffy &= ~loopbit;
164                 }
165
166                 /* Round the value and print it */
167                 printk("%lu.%02lu BogoMIPS (lpj=%lu)\n",
168                         loops_per_jiffy/(500000/HZ),
169                         (loops_per_jiffy/(5000/HZ)) % 100,
170                         loops_per_jiffy);
171         }
172
173 }