Annotation of prex/dev/power/cpufreq.c, Revision 1.1.1.1
1.1 nbrk 1: /*-
2: * Copyright (c) 2007-2008, Kohsuke Ohtani
3: * All rights reserved.
4: *
5: * Redistribution and use in source and binary forms, with or without
6: * modification, are permitted provided that the following conditions
7: * are met:
8: * 1. Redistributions of source code must retain the above copyright
9: * notice, this list of conditions and the following disclaimer.
10: * 2. Redistributions in binary form must reproduce the above copyright
11: * notice, this list of conditions and the following disclaimer in the
12: * documentation and/or other materials provided with the distribution.
13: * 3. Neither the name of the author nor the names of any co-contributors
14: * may be used to endorse or promote products derived from this software
15: * without specific prior written permission.
16: *
17: * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
18: * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19: * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20: * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
21: * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
22: * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
23: * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
24: * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
25: * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
26: * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
27: * SUCH DAMAGE.
28: */
29:
30: /*
31: * cpufreq.c - CPU frequency control
32: */
33:
34: /*
35: * Dynamic voltage scaling (DVS)
36: *
37: * DVS is widely used with mobile systems to save the processor
38: * power consumption, with minimum impact on performance.
39: * The basic idea is come from the fact the power consumption is
40: * proportional to V^2 x f, where V is voltage and f is frequency.
41: * Since processor does not always require the full performance,
42: * we can reduce power consumption by lowering voltage and frequeceny.
43: */
44:
45: #include <sys/ioctl.h>
46: #include <driver.h>
47: #include <pm.h>
48: #include <cpu.h>
49: #include <cpufreq.h>
50:
51: /* #define DEBUG_CPUFREQ 1 */
52:
53: #ifdef DEBUG_CPUFREQ
54: #define DPRINTF(a) printf a
55: #else
56: #define DPRINTF(a)
57: #endif
58:
59: /*
60: * DVS parameters
61: */
62: #define INTERVAL_MSEC 50
63: #define INTERVAL_TICK msec_to_tick(INTERVAL_MSEC)
64: #define WEIGHT 20
65:
66: static int cpufreq_open(device_t dev, int mode);
67: static int cpufreq_ioctl(device_t dev, u_long cmd, void *arg);
68: static int cpufreq_close(device_t dev);
69: static int cpufreq_init(void);
70:
71: /*
72: * Driver structure
73: */
74: struct driver cpufreq_drv = {
75: /* name */ "CPU Frequency Control",
76: /* order */ 3, /* Must larger than pm driver */
77: /* init */ cpufreq_init,
78: };
79:
80: /*
81: * Device I/O table
82: */
83: static struct devio cpufreq_io = {
84: /* open */ cpufreq_open,
85: /* close */ cpufreq_close,
86: /* read */ NULL,
87: /* write */ NULL,
88: /* ioctl */ cpufreq_ioctl,
89: /* event */ NULL,
90: };
91:
92: static device_t cpufreq_dev; /* Device object */
93:
94: static int cpufreq_policy; /* Frequecy control policy */
95:
96: static struct dpc dvs_dpc; /* DPC object */
97:
98: static int dvs_capable; /* True if the system has dvs capability */
99: static int dvs_enabled; /* True if dvs is enabled */
100:
101: static int cur_speed; /* Current CPU speed (%) */
102: static int max_speed; /* Maximum CPU speed (%) */
103: static int min_speed; /* Minimum CPU speed (%) */
104:
105: static int run_cycles; /* The non-idle CPU cycles in the last interval */
106: static int idle_cycles; /* The idle CPU cycles in the last interval */
107: static int excess_cycles; /* The cycles left over from the last interval */
108:
109: static int avg_workload; /* Average workload */
110: static int avg_deadline; /* Average deadline */
111:
112: static u_long elapsed_ticks;
113:
114:
115: /*
116: * Predict CPU speed.
117: *
118: * DVS Algorithm: Weiser Style
119: *
120: * If the utilization prediction x is high (over 70%), increase the
121: * speed by 20% of the maximum speed. If the utilization prediction
122: * is low (under 50%), decrease the speed by (60 - x)% of the
123: * maximum speed.
124: *
125: * excess_cycles is defined as the number of uncompleted run cycles
126: * from the last interval. For example, if we find 70% activity
127: * when runnig at full speed, and their processor speed was set to
128: * 50% during that interval, excess_cycles is set to 20%. This
129: * value (20%) is used to calculate the processor speed in the next
130: * interval.
131: *
132: * Refernce:
133: * M.Weiser, B.Welch, A.Demers, and S.Shenker,
134: * "Scheduling for Reduced CPU Energy", In Proceedings of the
135: * 1st Symposium on Operating Systems Design and Implementation,
136: * pages 13-23, November 1994.
137: */
138: static int
139: predict_cpu_speed(int speed)
140: {
141: int next_excess;
142: int run_percent;
143: int newspeed = speed;
144:
145: run_cycles += excess_cycles;
146: run_percent = (run_cycles * 100) / (idle_cycles + run_cycles);
147:
148: next_excess = run_cycles - speed * (run_cycles + idle_cycles) / 100;
149: if (next_excess < 0)
150: next_excess = 0;
151:
152: if (excess_cycles > idle_cycles)
153: newspeed = 100;
154: else if (run_percent > 70)
155: newspeed = speed + 20;
156: else if (run_percent < 50)
157: newspeed = speed - (60 - run_percent);
158:
159: if (newspeed > max_speed)
160: newspeed = max_speed;
161: if (newspeed < min_speed)
162: newspeed = min_speed;
163:
164: DPRINTF(("DVS: run_percent=%d next_excess=%d newspeed=%d\n\n",
165: run_percent, next_excess, newspeed));
166:
167: excess_cycles = next_excess;
168: return newspeed;
169: }
170:
171: /*
172: * Predict max CPU speed.
173: *
174: * DVS Algorithm: AVG<3>
175: *
176: * Computes an exponentially moving average of the previous intervals.
177: * <wight> is the relative weighting of past intervals relative to
178: * the current interval.
179: *
180: * predict = (weight x current + past) / (weight + 1)
181: *
182: * Refernce:
183: * K.Govil, E.Chan, H.Wasserman,
184: * "Comparing Algorithm for Dynamic Speed-Setting of a Low-Power CPU".
185: * Proc. 1st Int'l Conference on Mobile Computing and Networking,
186: * Nov 1995.
187: */
188: static int
189: predict_max_speed(int speed)
190: {
191: int new_workload;
192: int new_deadline;
193: int newspeed;
194:
195: new_workload = run_cycles * speed;
196: new_deadline = (run_cycles + idle_cycles) * speed;
197:
198: avg_workload = (avg_workload * WEIGHT + new_workload) / (WEIGHT + 1);
199: avg_deadline = (avg_deadline * WEIGHT + new_deadline) / (WEIGHT + 1);
200:
201: newspeed = avg_workload * 100 / avg_deadline;
202:
203: DPRINTF(("DVS: new_workload=%u new_deadline=%u\n",
204: new_workload, new_deadline));
205: DPRINTF(("DVS: avg_workload=%u avg_deadline=%u\n",
206: avg_workload, avg_deadline));
207: return newspeed;
208: }
209:
210: /*
211: * DPC routine to set CPU speed.
212: *
213: * This is kicked by dvs_tick() if it needed.
214: */
215: static void
216: dpc_adjust_speed(void *arg)
217: {
218: int newspeed = (int)arg;
219:
220: DPRINTF(("DVS: new speed=%d\n", newspeed));
221: cpu_setperf(newspeed);
222: cur_speed = cpu_getperf();
223: }
224:
225: /*
226: * Timer hook routine called by tick handler.
227: */
228: static void
229: dvs_tick(int idle)
230: {
231: int newspeed;
232:
233: elapsed_ticks++;
234: if (idle)
235: idle_cycles++;
236: else
237: run_cycles++;
238:
239: if (elapsed_ticks < INTERVAL_TICK)
240: return;
241:
242: /* Predict max CPU speed */
243: max_speed = predict_max_speed(cur_speed);
244:
245: DPRINTF(("DVS: run_cycles=%d idle_cycles=%d cur_speed=%d "
246: "max_speed=%d\n",
247: run_cycles, idle_cycles, cur_speed, max_speed));
248: /*
249: * Predict next CPU speed
250: */
251: newspeed = predict_cpu_speed(cur_speed);
252: if (newspeed != cur_speed) {
253: sched_dpc(&dvs_dpc, &dpc_adjust_speed, (void *)newspeed);
254: }
255: run_cycles = 0;
256: idle_cycles = 0;
257: elapsed_ticks = 0;
258: }
259:
260: /*
261: * Enable DVS operation
262: */
263: static void
264: dvs_enable(void)
265: {
266:
267: if (!dvs_capable)
268: return;
269:
270: run_cycles = 0;
271: idle_cycles = 0;
272: elapsed_ticks = 0;
273:
274: max_speed = 100; /* max 100% */
275: min_speed = 5; /* min 5% */
276: cur_speed = cpu_getperf();
277:
278: timer_hook(dvs_tick);
279: dvs_enabled = 1;
280: }
281:
282: /*
283: * Disable DVS operation
284: */
285: static void
286: dvs_disable(void)
287: {
288:
289: if (!dvs_capable)
290: return;
291:
292: timer_hook(NULL);
293:
294: /* Set CPU speed to 100% */
295: cpu_setperf(100);
296: dvs_enabled = 0;
297: }
298:
299: static int
300: cpufreq_open(device_t dev, int mode)
301: {
302:
303: return 0;
304: }
305:
306: static int
307: cpufreq_close(device_t dev)
308: {
309:
310: return 0;
311: }
312:
313: static int
314: cpufreq_ioctl(device_t dev, u_long cmd, void *arg)
315: {
316:
317: return 0;
318: }
319:
320: void
321: cpufreq_setpolicy(int policy)
322: {
323:
324: switch (cpufreq_policy) {
325: case CPUFREQ_ONDEMAND:
326: if (policy == PM_POWERSAVE)
327: dvs_enable();
328: else
329: dvs_disable();
330:
331: break;
332: case CPUFREQ_MAXSPEED:
333: break;
334: case CPUFREQ_MINSPEED:
335: break;
336: }
337: }
338:
339: static int
340: cpufreq_init(void)
341: {
342: int policy;
343:
344: if (cpu_initperf())
345: return -1;
346:
347: /* Create device object */
348: cpufreq_dev = device_create(&cpufreq_io, "cpufreq", DF_CHR);
349: ASSERT(cpufreq_dev);
350:
351: dvs_capable = 1;
352:
353: policy = pm_getpolicy();
354: if (policy == PM_POWERSAVE)
355: dvs_enable();
356: return 0;
357: }
358:
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