Annotation of prex/dev/power/cpufreq.c, Revision 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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