blob: 2568d22a304ecc667b302b0b5d17956ed6d143a8 [file] [log] [blame]
Linus Torvalds1da177e2005-04-16 15:20:36 -07001/* calibrate.c: default delay calibration
2 *
3 * Excised from init/main.c
4 * Copyright (C) 1991, 1992 Linus Torvalds
5 */
6
Tim Schmielaucd354f12007-02-14 00:33:14 -08007#include <linux/jiffies.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -07008#include <linux/delay.h>
9#include <linux/init.h>
Andrew Morton941e4922008-02-06 01:36:42 -080010#include <linux/timex.h>
Alok Kataria3da757d2008-06-20 15:06:33 -070011#include <linux/smp.h>
Venkatesh Pallipadi8a9e1b02005-06-23 00:08:13 -070012
Alok Katariaf3f31492008-06-23 18:21:56 -070013unsigned long lpj_fine;
Randy Dunlapbfe8df32007-10-16 01:23:46 -070014unsigned long preset_lpj;
Linus Torvalds1da177e2005-04-16 15:20:36 -070015static int __init lpj_setup(char *str)
16{
17 preset_lpj = simple_strtoul(str,NULL,0);
18 return 1;
19}
20
21__setup("lpj=", lpj_setup);
22
Venkatesh Pallipadi8a9e1b02005-06-23 00:08:13 -070023#ifdef ARCH_HAS_READ_CURRENT_TIMER
24
25/* This routine uses the read_current_timer() routine and gets the
26 * loops per jiffy directly, instead of guessing it using delay().
27 * Also, this code tries to handle non-maskable asynchronous events
28 * (like SMIs)
29 */
30#define DELAY_CALIBRATION_TICKS ((HZ < 100) ? 1 : (HZ/100))
31#define MAX_DIRECT_CALIBRATION_RETRIES 5
32
Adrian Bunk6c81c322008-02-06 01:37:51 -080033static unsigned long __cpuinit calibrate_delay_direct(void)
Venkatesh Pallipadi8a9e1b02005-06-23 00:08:13 -070034{
35 unsigned long pre_start, start, post_start;
36 unsigned long pre_end, end, post_end;
37 unsigned long start_jiffies;
Alok Katariaf3f31492008-06-23 18:21:56 -070038 unsigned long timer_rate_min, timer_rate_max;
39 unsigned long good_timer_sum = 0;
40 unsigned long good_timer_count = 0;
Andrew Worsleyd2b46312011-05-24 17:13:15 -070041 unsigned long measured_times[MAX_DIRECT_CALIBRATION_RETRIES];
42 int max = -1; /* index of measured_times with max/min values or not set */
43 int min = -1;
Venkatesh Pallipadi8a9e1b02005-06-23 00:08:13 -070044 int i;
45
46 if (read_current_timer(&pre_start) < 0 )
47 return 0;
48
49 /*
50 * A simple loop like
51 * while ( jiffies < start_jiffies+1)
52 * start = read_current_timer();
53 * will not do. As we don't really know whether jiffy switch
54 * happened first or timer_value was read first. And some asynchronous
55 * event can happen between these two events introducing errors in lpj.
56 *
57 * So, we do
58 * 1. pre_start <- When we are sure that jiffy switch hasn't happened
59 * 2. check jiffy switch
60 * 3. start <- timer value before or after jiffy switch
61 * 4. post_start <- When we are sure that jiffy switch has happened
62 *
63 * Note, we don't know anything about order of 2 and 3.
64 * Now, by looking at post_start and pre_start difference, we can
65 * check whether any asynchronous event happened or not
66 */
67
68 for (i = 0; i < MAX_DIRECT_CALIBRATION_RETRIES; i++) {
69 pre_start = 0;
70 read_current_timer(&start);
71 start_jiffies = jiffies;
Tim Deegan70a06222011-02-10 08:50:41 +000072 while (time_before_eq(jiffies, start_jiffies + 1)) {
Venkatesh Pallipadi8a9e1b02005-06-23 00:08:13 -070073 pre_start = start;
74 read_current_timer(&start);
75 }
76 read_current_timer(&post_start);
77
78 pre_end = 0;
79 end = post_start;
Tim Deegan70a06222011-02-10 08:50:41 +000080 while (time_before_eq(jiffies, start_jiffies + 1 +
81 DELAY_CALIBRATION_TICKS)) {
Venkatesh Pallipadi8a9e1b02005-06-23 00:08:13 -070082 pre_end = end;
83 read_current_timer(&end);
84 }
85 read_current_timer(&post_end);
86
Alok Katariaf3f31492008-06-23 18:21:56 -070087 timer_rate_max = (post_end - pre_start) /
88 DELAY_CALIBRATION_TICKS;
89 timer_rate_min = (pre_end - post_start) /
90 DELAY_CALIBRATION_TICKS;
Venkatesh Pallipadi8a9e1b02005-06-23 00:08:13 -070091
92 /*
Alok Katariaf3f31492008-06-23 18:21:56 -070093 * If the upper limit and lower limit of the timer_rate is
Venkatesh Pallipadi8a9e1b02005-06-23 00:08:13 -070094 * >= 12.5% apart, redo calibration.
95 */
Andrew Worsleyd2b46312011-05-24 17:13:15 -070096 if (start >= post_end)
97 printk(KERN_NOTICE "calibrate_delay_direct() ignoring "
98 "timer_rate as we had a TSC wrap around"
99 " start=%lu >=post_end=%lu\n",
100 start, post_end);
101 if (start < post_end && pre_start != 0 && pre_end != 0 &&
Alok Katariaf3f31492008-06-23 18:21:56 -0700102 (timer_rate_max - timer_rate_min) < (timer_rate_max >> 3)) {
103 good_timer_count++;
104 good_timer_sum += timer_rate_max;
Andrew Worsleyd2b46312011-05-24 17:13:15 -0700105 measured_times[i] = timer_rate_max;
106 if (max < 0 || timer_rate_max > measured_times[max])
107 max = i;
108 if (min < 0 || timer_rate_max < measured_times[min])
109 min = i;
110 } else
111 measured_times[i] = 0;
112
Venkatesh Pallipadi8a9e1b02005-06-23 00:08:13 -0700113 }
114
Andrew Worsleyd2b46312011-05-24 17:13:15 -0700115 /*
116 * Find the maximum & minimum - if they differ too much throw out the
117 * one with the largest difference from the mean and try again...
118 */
119 while (good_timer_count > 1) {
120 unsigned long estimate;
121 unsigned long maxdiff;
Venkatesh Pallipadi8a9e1b02005-06-23 00:08:13 -0700122
Andrew Worsleyd2b46312011-05-24 17:13:15 -0700123 /* compute the estimate */
124 estimate = (good_timer_sum/good_timer_count);
125 maxdiff = estimate >> 3;
126
127 /* if range is within 12% let's take it */
128 if ((measured_times[max] - measured_times[min]) < maxdiff)
129 return estimate;
130
131 /* ok - drop the worse value and try again... */
132 good_timer_sum = 0;
133 good_timer_count = 0;
134 if ((measured_times[max] - estimate) <
135 (estimate - measured_times[min])) {
136 printk(KERN_NOTICE "calibrate_delay_direct() dropping "
137 "min bogoMips estimate %d = %lu\n",
138 min, measured_times[min]);
139 measured_times[min] = 0;
140 min = max;
141 } else {
142 printk(KERN_NOTICE "calibrate_delay_direct() dropping "
143 "max bogoMips estimate %d = %lu\n",
144 max, measured_times[max]);
145 measured_times[max] = 0;
146 max = min;
147 }
148
149 for (i = 0; i < MAX_DIRECT_CALIBRATION_RETRIES; i++) {
150 if (measured_times[i] == 0)
151 continue;
152 good_timer_count++;
153 good_timer_sum += measured_times[i];
154 if (measured_times[i] < measured_times[min])
155 min = i;
156 if (measured_times[i] > measured_times[max])
157 max = i;
158 }
159
160 }
161
162 printk(KERN_NOTICE "calibrate_delay_direct() failed to get a good "
163 "estimate for loops_per_jiffy.\nProbably due to long platform "
164 "interrupts. Consider using \"lpj=\" boot option.\n");
Venkatesh Pallipadi8a9e1b02005-06-23 00:08:13 -0700165 return 0;
166}
167#else
Adrian Bunk6c81c322008-02-06 01:37:51 -0800168static unsigned long __cpuinit calibrate_delay_direct(void) {return 0;}
Venkatesh Pallipadi8a9e1b02005-06-23 00:08:13 -0700169#endif
170
Linus Torvalds1da177e2005-04-16 15:20:36 -0700171/*
172 * This is the number of bits of precision for the loops_per_jiffy. Each
Phil Carmody191e5682011-03-22 16:34:13 -0700173 * time we refine our estimate after the first takes 1.5/HZ seconds, so try
174 * to start with a good estimate.
Alok Kataria3da757d2008-06-20 15:06:33 -0700175 * For the boot cpu we can skip the delay calibration and assign it a value
Alok Katariaf3f31492008-06-23 18:21:56 -0700176 * calculated based on the timer frequency.
177 * For the rest of the CPUs we cannot assume that the timer frequency is same as
Alok Kataria3da757d2008-06-20 15:06:33 -0700178 * the cpu frequency, hence do the calibration for those.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700179 */
180#define LPS_PREC 8
181
Phil Carmody71c696b2011-03-22 16:34:12 -0700182static unsigned long __cpuinit calibrate_delay_converge(void)
183{
Phil Carmody191e5682011-03-22 16:34:13 -0700184 /* First stage - slowly accelerate to find initial bounds */
Phil Carmodyb1b5f652011-03-22 16:34:15 -0700185 unsigned long lpj, lpj_base, ticks, loopadd, loopadd_base, chop_limit;
Phil Carmody191e5682011-03-22 16:34:13 -0700186 int trials = 0, band = 0, trial_in_band = 0;
Phil Carmody71c696b2011-03-22 16:34:12 -0700187
188 lpj = (1<<12);
Phil Carmody191e5682011-03-22 16:34:13 -0700189
190 /* wait for "start of" clock tick */
191 ticks = jiffies;
192 while (ticks == jiffies)
193 ; /* nothing */
194 /* Go .. */
195 ticks = jiffies;
196 do {
197 if (++trial_in_band == (1<<band)) {
198 ++band;
199 trial_in_band = 0;
200 }
201 __delay(lpj * band);
202 trials += band;
203 } while (ticks == jiffies);
204 /*
205 * We overshot, so retreat to a clear underestimate. Then estimate
206 * the largest likely undershoot. This defines our chop bounds.
207 */
208 trials -= band;
Phil Carmodyb1b5f652011-03-22 16:34:15 -0700209 loopadd_base = lpj * band;
210 lpj_base = lpj * trials;
211
212recalibrate:
213 lpj = lpj_base;
214 loopadd = loopadd_base;
Phil Carmody71c696b2011-03-22 16:34:12 -0700215
216 /*
217 * Do a binary approximation to get lpj set to
Phil Carmody191e5682011-03-22 16:34:13 -0700218 * equal one clock (up to LPS_PREC bits)
Phil Carmody71c696b2011-03-22 16:34:12 -0700219 */
Phil Carmodyb1b5f652011-03-22 16:34:15 -0700220 chop_limit = lpj >> LPS_PREC;
Phil Carmody191e5682011-03-22 16:34:13 -0700221 while (loopadd > chop_limit) {
222 lpj += loopadd;
Phil Carmody71c696b2011-03-22 16:34:12 -0700223 ticks = jiffies;
224 while (ticks == jiffies)
Phil Carmody191e5682011-03-22 16:34:13 -0700225 ; /* nothing */
Phil Carmody71c696b2011-03-22 16:34:12 -0700226 ticks = jiffies;
227 __delay(lpj);
228 if (jiffies != ticks) /* longer than 1 tick */
Phil Carmody191e5682011-03-22 16:34:13 -0700229 lpj -= loopadd;
230 loopadd >>= 1;
Phil Carmody71c696b2011-03-22 16:34:12 -0700231 }
Phil Carmodyb1b5f652011-03-22 16:34:15 -0700232 /*
233 * If we incremented every single time possible, presume we've
234 * massively underestimated initially, and retry with a higher
235 * start, and larger range. (Only seen on x86_64, due to SMIs)
236 */
237 if (lpj + loopadd * 2 == lpj_base + loopadd_base * 2) {
238 lpj_base = lpj;
239 loopadd_base <<= 2;
240 goto recalibrate;
241 }
Phil Carmody71c696b2011-03-22 16:34:12 -0700242
243 return lpj;
244}
245
Adrian Bunk6c81c322008-02-06 01:37:51 -0800246void __cpuinit calibrate_delay(void)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700247{
Mike Travisfeae3202009-11-17 18:22:13 -0600248 static bool printed;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700249
250 if (preset_lpj) {
251 loops_per_jiffy = preset_lpj;
Mike Travisfeae3202009-11-17 18:22:13 -0600252 if (!printed)
253 pr_info("Calibrating delay loop (skipped) "
254 "preset value.. ");
255 } else if ((!printed) && lpj_fine) {
Alok Katariaf3f31492008-06-23 18:21:56 -0700256 loops_per_jiffy = lpj_fine;
Mike Travisfeae3202009-11-17 18:22:13 -0600257 pr_info("Calibrating delay loop (skipped), "
Alok Katariaf3f31492008-06-23 18:21:56 -0700258 "value calculated using timer frequency.. ");
Venkatesh Pallipadi8a9e1b02005-06-23 00:08:13 -0700259 } else if ((loops_per_jiffy = calibrate_delay_direct()) != 0) {
Mike Travisfeae3202009-11-17 18:22:13 -0600260 if (!printed)
261 pr_info("Calibrating delay using timer "
262 "specific routine.. ");
Linus Torvalds1da177e2005-04-16 15:20:36 -0700263 } else {
Mike Travisfeae3202009-11-17 18:22:13 -0600264 if (!printed)
265 pr_info("Calibrating delay loop... ");
Phil Carmody71c696b2011-03-22 16:34:12 -0700266 loops_per_jiffy = calibrate_delay_converge();
Linus Torvalds1da177e2005-04-16 15:20:36 -0700267 }
Mike Travisfeae3202009-11-17 18:22:13 -0600268 if (!printed)
269 pr_cont("%lu.%02lu BogoMIPS (lpj=%lu)\n",
Alok Kataria3da757d2008-06-20 15:06:33 -0700270 loops_per_jiffy/(500000/HZ),
271 (loops_per_jiffy/(5000/HZ)) % 100, loops_per_jiffy);
Mike Travisfeae3202009-11-17 18:22:13 -0600272
273 printed = true;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700274}