FastThread.cpp revision 6d8018f0b7be9deec6b0acab10a0dca6e91d0fb8 
1/*
2 * Copyright (C) 2014 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17#define LOG_TAG "FastThread"
18//#define LOG_NDEBUG 0
19
20#define ATRACE_TAG ATRACE_TAG_AUDIO
21
22#include "Configuration.h"
23#include <linux/futex.h>
24#include <sys/syscall.h>
25#include <cutils/atomic.h>
26#include <utils/Log.h>
27#include <utils/Trace.h>
28#include "FastThread.h"
29#include "FastThreadDumpState.h"
30
31#define FAST_DEFAULT_NS    999999999L   // ~1 sec: default time to sleep
32#define FAST_HOT_IDLE_NS     1000000L   // 1 ms: time to sleep while hot idling
33#define MIN_WARMUP_CYCLES          2    // minimum number of consecutive in-range loop cycles
34                                        // to wait for warmup
35#define MAX_WARMUP_CYCLES         10    // maximum number of loop cycles to wait for warmup
36
37namespace android {
38
39FastThread::FastThread(const char *cycleMs, const char *loadUs) : Thread(false /*canCallJava*/),
40    // re-initialized to &sInitial by subclass constructor
41    mPrevious(NULL), mCurrent(NULL),
42    /* mOldTs({0, 0}), */
43    mOldTsValid(false),
44    mSleepNs(-1),
45    mPeriodNs(0),
46    mUnderrunNs(0),
47    mOverrunNs(0),
48    mForceNs(0),
49    mWarmupNsMin(0),
50    mWarmupNsMax(LONG_MAX),
51    // re-initialized to &mDummySubclassDumpState by subclass constructor
52    mDummyDumpState(NULL),
53    mDumpState(NULL),
54    mIgnoreNextOverrun(true),
55#ifdef FAST_THREAD_STATISTICS
56    // mOldLoad
57    mOldLoadValid(false),
58    mBounds(0),
59    mFull(false),
60    // mTcu
61#endif
62    mColdGen(0),
63    mIsWarm(false),
64    /* mMeasuredWarmupTs({0, 0}), */
65    mWarmupCycles(0),
66    mWarmupConsecutiveInRangeCycles(0),
67    // mDummyLogWriter
68    mLogWriter(&mDummyLogWriter),
69    mTimestampStatus(INVALID_OPERATION),
70
71    mCommand(FastThreadState::INITIAL),
72#if 0
73    frameCount(0),
74#endif
75    mAttemptedWrite(false)
76    // mCycleMs(cycleMs)
77    // mLoadUs(loadUs)
78{
79    mOldTs.tv_sec = 0;
80    mOldTs.tv_nsec = 0;
81    mMeasuredWarmupTs.tv_sec = 0;
82    mMeasuredWarmupTs.tv_nsec = 0;
83    strlcpy(mCycleMs, cycleMs, sizeof(mCycleMs));
84    strlcpy(mLoadUs, loadUs, sizeof(mLoadUs));
85}
86
87FastThread::~FastThread()
88{
89}
90
91bool FastThread::threadLoop()
92{
93    for (;;) {
94
95        // either nanosleep, sched_yield, or busy wait
96        if (mSleepNs >= 0) {
97            if (mSleepNs > 0) {
98                ALOG_ASSERT(mSleepNs < 1000000000);
99                const struct timespec req = {0, mSleepNs};
100                nanosleep(&req, NULL);
101            } else {
102                sched_yield();
103            }
104        }
105        // default to long sleep for next cycle
106        mSleepNs = FAST_DEFAULT_NS;
107
108        // poll for state change
109        const FastThreadState *next = poll();
110        if (next == NULL) {
111            // continue to use the default initial state until a real state is available
112            // FIXME &sInitial not available, should save address earlier
113            //ALOG_ASSERT(mCurrent == &sInitial && previous == &sInitial);
114            next = mCurrent;
115        }
116
117        mCommand = next->mCommand;
118        if (next != mCurrent) {
119
120            // As soon as possible of learning of a new dump area, start using it
121            mDumpState = next->mDumpState != NULL ? next->mDumpState : mDummyDumpState;
122            mLogWriter = next->mNBLogWriter != NULL ? next->mNBLogWriter : &mDummyLogWriter;
123            setLog(mLogWriter);
124
125            // We want to always have a valid reference to the previous (non-idle) state.
126            // However, the state queue only guarantees access to current and previous states.
127            // So when there is a transition from a non-idle state into an idle state, we make a
128            // copy of the last known non-idle state so it is still available on return from idle.
129            // The possible transitions are:
130            //  non-idle -> non-idle    update previous from current in-place
131            //  non-idle -> idle        update previous from copy of current
132            //  idle     -> idle        don't update previous
133            //  idle     -> non-idle    don't update previous
134            if (!(mCurrent->mCommand & FastThreadState::IDLE)) {
135                if (mCommand & FastThreadState::IDLE) {
136                    onIdle();
137                    mOldTsValid = false;
138#ifdef FAST_THREAD_STATISTICS
139                    mOldLoadValid = false;
140#endif
141                    mIgnoreNextOverrun = true;
142                }
143                mPrevious = mCurrent;
144            }
145            mCurrent = next;
146        }
147#if !LOG_NDEBUG
148        next = NULL;    // not referenced again
149#endif
150
151        mDumpState->mCommand = mCommand;
152
153        // FIXME what does this comment mean?
154        // << current, previous, command, dumpState >>
155
156        switch (mCommand) {
157        case FastThreadState::INITIAL:
158        case FastThreadState::HOT_IDLE:
159            mSleepNs = FAST_HOT_IDLE_NS;
160            continue;
161        case FastThreadState::COLD_IDLE:
162            // only perform a cold idle command once
163            // FIXME consider checking previous state and only perform if previous != COLD_IDLE
164            if (mCurrent->mColdGen != mColdGen) {
165                int32_t *coldFutexAddr = mCurrent->mColdFutexAddr;
166                ALOG_ASSERT(coldFutexAddr != NULL);
167                int32_t old = android_atomic_dec(coldFutexAddr);
168                if (old <= 0) {
169                    syscall(__NR_futex, coldFutexAddr, FUTEX_WAIT_PRIVATE, old - 1, NULL);
170                }
171                int policy = sched_getscheduler(0) & ~SCHED_RESET_ON_FORK;
172                if (!(policy == SCHED_FIFO || policy == SCHED_RR)) {
173                    ALOGE("did not receive expected priority boost on time");
174                }
175                // This may be overly conservative; there could be times that the normal mixer
176                // requests such a brief cold idle that it doesn't require resetting this flag.
177                mIsWarm = false;
178                mMeasuredWarmupTs.tv_sec = 0;
179                mMeasuredWarmupTs.tv_nsec = 0;
180                mWarmupCycles = 0;
181                mWarmupConsecutiveInRangeCycles = 0;
182                mSleepNs = -1;
183                mColdGen = mCurrent->mColdGen;
184#ifdef FAST_THREAD_STATISTICS
185                mBounds = 0;
186                mFull = false;
187#endif
188                mOldTsValid = !clock_gettime(CLOCK_MONOTONIC, &mOldTs);
189                mTimestampStatus = INVALID_OPERATION;
190            } else {
191                mSleepNs = FAST_HOT_IDLE_NS;
192            }
193            continue;
194        case FastThreadState::EXIT:
195            onExit();
196            return false;
197        default:
198            LOG_ALWAYS_FATAL_IF(!isSubClassCommand(mCommand));
199            break;
200        }
201
202        // there is a non-idle state available to us; did the state change?
203        if (mCurrent != mPrevious) {
204            onStateChange();
205#if 1   // FIXME shouldn't need this
206            // only process state change once
207            mPrevious = mCurrent;
208#endif
209        }
210
211        // do work using current state here
212        mAttemptedWrite = false;
213        onWork();
214
215        // To be exactly periodic, compute the next sleep time based on current time.
216        // This code doesn't have long-term stability when the sink is non-blocking.
217        // FIXME To avoid drift, use the local audio clock or watch the sink's fill status.
218        struct timespec newTs;
219        int rc = clock_gettime(CLOCK_MONOTONIC, &newTs);
220        if (rc == 0) {
221            //mLogWriter->logTimestamp(newTs);
222            if (mOldTsValid) {
223                time_t sec = newTs.tv_sec - mOldTs.tv_sec;
224                long nsec = newTs.tv_nsec - mOldTs.tv_nsec;
225                ALOGE_IF(sec < 0 || (sec == 0 && nsec < 0),
226                        "clock_gettime(CLOCK_MONOTONIC) failed: was %ld.%09ld but now %ld.%09ld",
227                        mOldTs.tv_sec, mOldTs.tv_nsec, newTs.tv_sec, newTs.tv_nsec);
228                if (nsec < 0) {
229                    --sec;
230                    nsec += 1000000000;
231                }
232                // To avoid an initial underrun on fast tracks after exiting standby,
233                // do not start pulling data from tracks and mixing until warmup is complete.
234                // Warmup is considered complete after the earlier of:
235                //      MIN_WARMUP_CYCLES consecutive in-range write() attempts,
236                //          where "in-range" means mWarmupNsMin <= cycle time <= mWarmupNsMax
237                //      MAX_WARMUP_CYCLES write() attempts.
238                // This is overly conservative, but to get better accuracy requires a new HAL API.
239                if (!mIsWarm && mAttemptedWrite) {
240                    mMeasuredWarmupTs.tv_sec += sec;
241                    mMeasuredWarmupTs.tv_nsec += nsec;
242                    if (mMeasuredWarmupTs.tv_nsec >= 1000000000) {
243                        mMeasuredWarmupTs.tv_sec++;
244                        mMeasuredWarmupTs.tv_nsec -= 1000000000;
245                    }
246                    ++mWarmupCycles;
247                    if (mWarmupNsMin <= nsec && nsec <= mWarmupNsMax) {
248                        ALOGV("warmup cycle %d in range: %.03f ms", mWarmupCycles, nsec * 1e-9);
249                        ++mWarmupConsecutiveInRangeCycles;
250                    } else {
251                        ALOGV("warmup cycle %d out of range: %.03f ms", mWarmupCycles, nsec * 1e-9);
252                        mWarmupConsecutiveInRangeCycles = 0;
253                    }
254                    if ((mWarmupConsecutiveInRangeCycles >= MIN_WARMUP_CYCLES) ||
255                            (mWarmupCycles >= MAX_WARMUP_CYCLES)) {
256                        mIsWarm = true;
257                        mDumpState->mMeasuredWarmupTs = mMeasuredWarmupTs;
258                        mDumpState->mWarmupCycles = mWarmupCycles;
259                    }
260                }
261                mSleepNs = -1;
262                if (mIsWarm) {
263                    if (sec > 0 || nsec > mUnderrunNs) {
264                        ATRACE_NAME("underrun");
265                        // FIXME only log occasionally
266                        ALOGV("underrun: time since last cycle %d.%03ld sec",
267                                (int) sec, nsec / 1000000L);
268                        mDumpState->mUnderruns++;
269                        mIgnoreNextOverrun = true;
270                    } else if (nsec < mOverrunNs) {
271                        if (mIgnoreNextOverrun) {
272                            mIgnoreNextOverrun = false;
273                        } else {
274                            // FIXME only log occasionally
275                            ALOGV("overrun: time since last cycle %d.%03ld sec",
276                                    (int) sec, nsec / 1000000L);
277                            mDumpState->mOverruns++;
278                        }
279                        // This forces a minimum cycle time. It:
280                        //  - compensates for an audio HAL with jitter due to sample rate conversion
281                        //  - works with a variable buffer depth audio HAL that never pulls at a
282                        //    rate < than mOverrunNs per buffer.
283                        //  - recovers from overrun immediately after underrun
284                        // It doesn't work with a non-blocking audio HAL.
285                        mSleepNs = mForceNs - nsec;
286                    } else {
287                        mIgnoreNextOverrun = false;
288                    }
289                }
290#ifdef FAST_THREAD_STATISTICS
291                if (mIsWarm) {
292                    // advance the FIFO queue bounds
293                    size_t i = mBounds & (mDumpState->mSamplingN - 1);
294                    mBounds = (mBounds & 0xFFFF0000) | ((mBounds + 1) & 0xFFFF);
295                    if (mFull) {
296                        mBounds += 0x10000;
297                    } else if (!(mBounds & (mDumpState->mSamplingN - 1))) {
298                        mFull = true;
299                    }
300                    // compute the delta value of clock_gettime(CLOCK_MONOTONIC)
301                    uint32_t monotonicNs = nsec;
302                    if (sec > 0 && sec < 4) {
303                        monotonicNs += sec * 1000000000;
304                    }
305                    // compute raw CPU load = delta value of clock_gettime(CLOCK_THREAD_CPUTIME_ID)
306                    uint32_t loadNs = 0;
307                    struct timespec newLoad;
308                    rc = clock_gettime(CLOCK_THREAD_CPUTIME_ID, &newLoad);
309                    if (rc == 0) {
310                        if (mOldLoadValid) {
311                            sec = newLoad.tv_sec - mOldLoad.tv_sec;
312                            nsec = newLoad.tv_nsec - mOldLoad.tv_nsec;
313                            if (nsec < 0) {
314                                --sec;
315                                nsec += 1000000000;
316                            }
317                            loadNs = nsec;
318                            if (sec > 0 && sec < 4) {
319                                loadNs += sec * 1000000000;
320                            }
321                        } else {
322                            // first time through the loop
323                            mOldLoadValid = true;
324                        }
325                        mOldLoad = newLoad;
326                    }
327#ifdef CPU_FREQUENCY_STATISTICS
328                    // get the absolute value of CPU clock frequency in kHz
329                    int cpuNum = sched_getcpu();
330                    uint32_t kHz = mTcu.getCpukHz(cpuNum);
331                    kHz = (kHz << 4) | (cpuNum & 0xF);
332#endif
333                    // save values in FIFO queues for dumpsys
334                    // these stores #1, #2, #3 are not atomic with respect to each other,
335                    // or with respect to store #4 below
336                    mDumpState->mMonotonicNs[i] = monotonicNs;
337                    mDumpState->mLoadNs[i] = loadNs;
338#ifdef CPU_FREQUENCY_STATISTICS
339                    mDumpState->mCpukHz[i] = kHz;
340#endif
341                    // this store #4 is not atomic with respect to stores #1, #2, #3 above, but
342                    // the newest open & oldest closed halves are atomic with respect to each other
343                    mDumpState->mBounds = mBounds;
344                    ATRACE_INT(mCycleMs, monotonicNs / 1000000);
345                    ATRACE_INT(mLoadUs, loadNs / 1000);
346                }
347#endif
348            } else {
349                // first time through the loop
350                mOldTsValid = true;
351                mSleepNs = mPeriodNs;
352                mIgnoreNextOverrun = true;
353            }
354            mOldTs = newTs;
355        } else {
356            // monotonic clock is broken
357            mOldTsValid = false;
358            mSleepNs = mPeriodNs;
359        }
360
361    }   // for (;;)
362
363    // never return 'true'; Thread::_threadLoop() locks mutex which can result in priority inversion
364}
365
366}   // namespace android
367