Annotation of prex-old/dev/power/dvs.c, Revision 1.1
1.1 ! nbrk 1: /*-
! 2: * Copyright (c) 2007, 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: * dvs.c - dynamic voltage scaling feature
! 32: */
! 33:
! 34: /*
! 35: * Dynamic voltage scaling (DVS) is widely used with mobile systems
! 36: * to save the processor power consumption, with minimum impact on
! 37: * performance. The basic idea is come from the fact the power
! 38: * consumption is proportional to V^2 x f, where V is voltage and
! 39: * f is frequency. Since processor does not always require the full
! 40: * performance, we can reduce power consumption by lowering voltage
! 41: * and frequeceny.
! 42: */
! 43: #include <driver.h>
! 44: #include <pm.h>
! 45: #include "dvs.h"
! 46:
! 47: /* #define DEBUG_DVS 1 */
! 48:
! 49: #ifdef DEBUG_DVS
! 50: #define dvs_printf(fmt, args...) printk("dvs: " fmt, ## args)
! 51: #else
! 52: #define dvs_printf(fmt...) do {} while (0)
! 53: #endif
! 54:
! 55: #define INTERVAL_MSEC 50
! 56: #define INTERVAL_TICK msec_to_tick(INTERVAL_MSEC)
! 57: #define WEIGHT 20
! 58:
! 59: static struct dpc dvs_dpc; /* DVC object */
! 60:
! 61: static int dvs_capable; /* True if the system has dvs capability */
! 62: static int dvs_enabled; /* True if dvs is enabled */
! 63:
! 64: static int cur_speed; /* Current CPU speed (%) */
! 65: static int max_speed; /* Maximum CPU speed (%) */
! 66: static int min_speed; /* Minimum CPU speed (%) */
! 67:
! 68: static int run_cycles; /* The non-idle CPU cycles in the last interval */
! 69: static int idle_cycles; /* The idle CPU cycles in the last interval */
! 70: static int excess_cycles; /* The cycles left over from the last interval */
! 71:
! 72: static int avg_workload; /* Average workload */
! 73: static int avg_deadline; /* Average deadline */
! 74:
! 75: static u_long elapsed_ticks;
! 76:
! 77: /*
! 78: * Predict CPU speed
! 79: *
! 80: * DVS Algorithm: Weiser Style
! 81: *
! 82: * If the utilization prediction x is high (over 70%), increase the speed
! 83: * by 20% of the maximum speed. If the utilization prediction is low
! 84: * (under 50%), decrease the speed by (60 - x)% of the maximum speed.
! 85: *
! 86: * excess_cycles is defined as the number of uncompleted run cycles from
! 87: * the last interval. For example, if we find 70% activity when runnig
! 88: * at full speed, and their processor speed was set to 50% during that
! 89: * interval, excess_cycles is set to 20%. This value (20%) is used to
! 90: * calculate the processor speed in the next interval.
! 91: *
! 92: * Refernce:
! 93: * M.Weiser, B.Welch, A.Demers, and S.Shenker,
! 94: * "Scheduling for Reduced CPU Energy", In Proceedings of the
! 95: * 1st Symposium on Operating Systems Design and Implementation,
! 96: * pages 13-23, November 1994.
! 97: */
! 98: static int
! 99: predict_cpu_speed(int speed)
! 100: {
! 101: int next_excess;
! 102: int run_percent;
! 103: int newspeed = speed;
! 104:
! 105: run_cycles += excess_cycles;
! 106: run_percent = (run_cycles * 100) / (idle_cycles + run_cycles);
! 107:
! 108: next_excess = run_cycles - speed * (run_cycles + idle_cycles) / 100;
! 109: if (next_excess < 0)
! 110: next_excess = 0;
! 111:
! 112: if (excess_cycles > idle_cycles)
! 113: newspeed = 100;
! 114: else if (run_percent > 70)
! 115: newspeed = speed + 20;
! 116: else if (run_percent < 50)
! 117: newspeed = speed - (60 - run_percent);
! 118:
! 119: if (newspeed > max_speed)
! 120: newspeed = max_speed;
! 121: if (newspeed < min_speed)
! 122: newspeed = min_speed;
! 123:
! 124: dvs_printf("run_percent=%d next_excess=%d newspeed=%d\n\n",
! 125: run_percent, next_excess, newspeed);
! 126:
! 127: excess_cycles = next_excess;
! 128: return newspeed;
! 129: }
! 130:
! 131: /*
! 132: * Predict max CPU speed
! 133: *
! 134: * DVS Algorithm: AVG<3>
! 135: *
! 136: * Computes an exponentially moving average of the previous intervals.
! 137: * <wight> is the relative wighting of past intervals relative to
! 138: * the current interval.
! 139: *
! 140: * predict = (weight x current + past) / (weight + 1)
! 141: *
! 142: * Refernce:
! 143: * K.Govil, E.Chan, H.Wasserman,
! 144: * "Comparing Algorithm for Dynamic Speed-Setting of a Low-Power CPU".
! 145: * Proc. 1st Int'l Conference on Mobile Computing and Networking, Nov 1995.
! 146: */
! 147: static int
! 148: predict_max_speed(int speed)
! 149: {
! 150: int new_workload;
! 151: int new_deadline;
! 152: int newspeed;
! 153:
! 154: new_workload = run_cycles * speed;
! 155: new_deadline = (run_cycles + idle_cycles) * speed;
! 156:
! 157: avg_workload = (avg_workload * WEIGHT + new_workload) / (WEIGHT + 1);
! 158: avg_deadline = (avg_deadline * WEIGHT + new_deadline) / (WEIGHT + 1);
! 159:
! 160: newspeed = avg_workload * 100 / avg_deadline;
! 161:
! 162: dvs_printf("new_workload=%u new_deadline=%u\n",
! 163: new_workload, new_deadline);
! 164: dvs_printf("avg_workload=%u avg_deadline=%u\n",
! 165: avg_workload, avg_deadline);
! 166: return newspeed;
! 167: }
! 168:
! 169: /*
! 170: * DPC routine to set CPU speed.
! 171: */
! 172: static void
! 173: dpc_adjust_speed(void *arg)
! 174: {
! 175: int newspeed = (int)arg;
! 176:
! 177: dvs_printf("dvs_adjust_speed: speed=%d\n", newspeed);
! 178: cpu_setperf(newspeed);
! 179: cur_speed = cpu_getperf();
! 180: }
! 181:
! 182: /*
! 183: * Timer hook routine called by tick handler.
! 184: */
! 185: static void
! 186: dvs_tick(int idle)
! 187: {
! 188: int newspeed;
! 189:
! 190: elapsed_ticks++;
! 191: if (idle)
! 192: idle_cycles++;
! 193: else
! 194: run_cycles++;
! 195:
! 196: if (elapsed_ticks < INTERVAL_TICK)
! 197: return;
! 198:
! 199: /* Predict max CPU speed */
! 200: max_speed = predict_max_speed(cur_speed);
! 201:
! 202: dvs_printf("DVS: run_cycles=%d idle_cycles=%d cur_speed=%d max_speed=%d\n",
! 203: run_cycles, idle_cycles, cur_speed, max_speed);
! 204: /*
! 205: * Predict next CPU speed
! 206: */
! 207: newspeed = predict_cpu_speed(cur_speed);
! 208: if (newspeed != cur_speed) {
! 209: sched_dpc(&dvs_dpc, dpc_adjust_speed,
! 210: (void *)newspeed);
! 211: }
! 212: run_cycles = 0;
! 213: idle_cycles = 0;
! 214: elapsed_ticks = 0;
! 215: }
! 216:
! 217: /*
! 218: * Enable DVS operation
! 219: */
! 220: void
! 221: dvs_enable(void)
! 222: {
! 223:
! 224: if (!dvs_capable)
! 225: return;
! 226:
! 227: run_cycles = 0;
! 228: idle_cycles = 0;
! 229: elapsed_ticks = 0;
! 230:
! 231: max_speed = 100; /* max 100% */
! 232: min_speed = 5; /* min 5% */
! 233: cur_speed = cpu_getperf();
! 234:
! 235: timer_hook(dvs_tick);
! 236: dvs_enabled = 1;
! 237: }
! 238:
! 239: /*
! 240: * Disable DVS operation
! 241: */
! 242: void
! 243: dvs_disable(void)
! 244: {
! 245:
! 246: if (!dvs_capable)
! 247: return;
! 248:
! 249: timer_hook(NULL);
! 250:
! 251: /* Set CPU speed to 100% */
! 252: cpu_setperf(100);
! 253: dvs_enabled = 0;
! 254: }
! 255:
! 256: /*
! 257: * Initialize dvs
! 258: */
! 259: void
! 260: dvs_init(void)
! 261: {
! 262:
! 263: if (cpu_initperf())
! 264: return;
! 265:
! 266: dvs_capable = 1;
! 267: }
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