t/read-to-pipe-async.c

   1 /*
   2  * Read a file and write the contents to stdout. If a given read takes
   3  * longer than 'max_us' time, then we schedule a new thread to handle
   4  * the next read. This avoids the coordinated omission problem, where
   5  * one request appears to take a long time, but in reality a lot of
   6  * requests would have been slow, but we don't notice since new submissions
   7  * are not being issued if just 1 is held up.
   8  *
   9  * One test case:
  10  *
  11  * $ time (./read-to-pipe-async -f randfile.gz | gzip -dc > outfile; sync)
  12  *
  13  * This will read randfile.gz and log the latencies of doing so, while
  14  * piping the output to gzip to decompress it. Any latencies over max_us
  15  * are logged when they happen, and latency buckets are displayed at the
  16  * end of the run
  17  *
  18  * gcc -Wall -g -O2 -o read-to-pipe-async read-to-pipe-async.c -lpthread
  19  *
  20  * Copyright (C) 2016 Jens Axboe
  21  *
  22  */
  23 #include <stdio.h>
  24 #include <stdlib.h>
  25 #include <unistd.h>
  26 #include <fcntl.h>
  27 #include <sys/time.h>
  28 #include <sys/types.h>
  29 #include <sys/stat.h>
  30 #include <inttypes.h>
  31 #include <string.h>
  32 #include <pthread.h>
  33 #include <errno.h>
  34 #include <assert.h>
  35 #include <time.h>
  36
  37 #include "../flist.h"
  38
  39 static int bs = 4096;
  40 static int max_us = 10000;
  41 static char *file;
  42 static int separate_writer = 1;
  43
  44 #define PLAT_BITS       8
  45 #define PLAT_VAL        (1 << PLAT_BITS)
  46 #define PLAT_GROUP_NR   19
  47 #define PLAT_NR         (PLAT_GROUP_NR * PLAT_VAL)
  48 #define PLAT_LIST_MAX   20
  49
  50 struct stats {
  51         unsigned int plat[PLAT_NR];
  52         unsigned int nr_samples;
  53         unsigned int max;
  54         unsigned int min;
  55         unsigned int over;
  56 };
  57
  58 static double plist[PLAT_LIST_MAX] = { 50.0, 75.0, 90.0, 95.0, 99.0, 99.5, 99.9, 99.99, 99.999, 99.9999, };
  59
  60 struct thread_data {
  61         int exit;
  62         int done;
  63         pthread_mutex_t lock;
  64         pthread_cond_t cond;
  65         pthread_mutex_t done_lock;
  66         pthread_cond_t done_cond;
  67         pthread_t thread;
  68 };
  69
  70 struct writer_thread {
  71         struct flist_head list;
  72         struct flist_head done_list;
  73         struct stats s;
  74         struct thread_data thread;
  75 };
  76
  77 struct reader_thread {
  78         struct flist_head list;
  79         struct flist_head done_list;
  80         int started;
  81         int busy;
  82         int write_seq;
  83         struct stats s;
  84         struct thread_data thread;
  85 };
  86
  87 struct work_item {
  88         struct flist_head list;
  89         void *buf;
  90         size_t buf_size;
  91         off_t off;
  92         int fd;
  93         int seq;
  94         struct writer_thread *writer;
  95         struct reader_thread *reader;
  96         pthread_mutex_t lock;
  97         pthread_cond_t cond;
  98         pthread_t thread;
  99 };
 100
 101 static struct reader_thread reader_thread;
 102 static struct writer_thread writer_thread;
 103
 104 uint64_t utime_since(const struct timeval *s, const struct timeval *e)
 105 {
 106         long sec, usec;
 107         uint64_t ret;
 108
 109         sec = e->tv_sec - s->tv_sec;
 110         usec = e->tv_usec - s->tv_usec;
 111         if (sec > 0 && usec < 0) {
 112                 sec--;
 113                 usec += 1000000;
 114         }
 115
 116         if (sec < 0 || (sec == 0 && usec < 0))
 117                 return 0;
 118
 119         ret = sec * 1000000ULL + usec;
 120
 121         return ret;
 122 }
 123
 124 static struct work_item *find_seq(struct writer_thread *w, unsigned int seq)
 125 {
 126         struct work_item *work;
 127         struct flist_head *entry;
 128
 129         if (flist_empty(&w->list))
 130                 return NULL;
 131
 132         flist_for_each(entry, &w->list) {
 133                 work = flist_entry(entry, struct work_item, list);
 134                 if (work->seq == seq)
 135                         return work;
 136         }
 137
 138         return NULL;
 139 }
 140
 141 static unsigned int plat_val_to_idx(unsigned int val)
 142 {
 143         unsigned int msb, error_bits, base, offset;
 144
 145         /* Find MSB starting from bit 0 */
 146         if (val == 0)
 147                 msb = 0;
 148         else
 149                 msb = sizeof(val)*8 - __builtin_clz(val) - 1;
 150
 151         /*
 152          * MSB <= (PLAT_BITS-1), cannot be rounded off. Use
 153          * all bits of the sample as index
 154          */
 155         if (msb <= PLAT_BITS)
 156                 return val;
 157
 158         /* Compute the number of error bits to discard*/
 159         error_bits = msb - PLAT_BITS;
 160
 161         /* Compute the number of buckets before the group */
 162         base = (error_bits + 1) << PLAT_BITS;
 163
 164         /*
 165          * Discard the error bits and apply the mask to find the
 166          * index for the buckets in the group
 167          */
 168         offset = (PLAT_VAL - 1) & (val >> error_bits);
 169
 170         /* Make sure the index does not exceed (array size - 1) */
 171         return (base + offset) < (PLAT_NR - 1) ?
 172                 (base + offset) : (PLAT_NR - 1);
 173 }
 174
 175 /*
 176  * Convert the given index of the bucket array to the value
 177  * represented by the bucket
 178  */
 179 static unsigned int plat_idx_to_val(unsigned int idx)
 180 {
 181         unsigned int error_bits, k, base;
 182
 183         assert(idx < PLAT_NR);
 184
 185         /* MSB <= (PLAT_BITS-1), cannot be rounded off. Use
 186          * all bits of the sample as index */
 187         if (idx < (PLAT_VAL << 1))
 188                 return idx;
 189
 190         /* Find the group and compute the minimum value of that group */
 191         error_bits = (idx >> PLAT_BITS) - 1;
 192         base = 1 << (error_bits + PLAT_BITS);
 193
 194         /* Find its bucket number of the group */
 195         k = idx % PLAT_VAL;
 196
 197         /* Return the mean of the range of the bucket */
 198         return base + ((k + 0.5) * (1 << error_bits));
 199 }
 200
 201 static void add_lat(struct stats *s, unsigned int us, const char *name)
 202 {
 203         int lat_index = 0;
 204
 205         if (us > s->max)
 206                 s->max = us;
 207         if (us < s->min)
 208                 s->min = us;
 209
 210         if (us > max_us) {
 211                 fprintf(stderr, "%s latency=%u usec\n", name, us);
 212                 s->over++;
 213         }
 214
 215         lat_index = plat_val_to_idx(us);
 216         __sync_fetch_and_add(&s->plat[lat_index], 1);
 217         __sync_fetch_and_add(&s->nr_samples, 1);
 218 }
 219
 220 static int write_work(struct work_item *work)
 221 {
 222         struct timeval s, e;
 223         ssize_t ret;
 224
 225         gettimeofday(&s, NULL);
 226         ret = write(STDOUT_FILENO, work->buf, work->buf_size);
 227         gettimeofday(&e, NULL);
 228         assert(ret == work->buf_size);
 229
 230         add_lat(&work->writer->s, utime_since(&s, &e), "write");
 231         return work->seq + 1;
 232 }
 233
 234 static void *writer_fn(void *data)
 235 {
 236         struct writer_thread *wt = data;
 237         struct work_item *work;
 238         unsigned int seq = 1;
 239
 240         work = NULL;
 241         while (!wt->thread.exit || !flist_empty(&wt->list)) {
 242                 pthread_mutex_lock(&wt->thread.lock);
 243
 244                 if (work) {
 245                         flist_add_tail(&work->list, &wt->done_list);
 246                         work = NULL;
 247                 }
 248
 249                 work = find_seq(wt, seq);
 250                 if (work)
 251                         flist_del_init(&work->list);
 252                 else
 253                         pthread_cond_wait(&wt->thread.cond, &wt->thread.lock);
 254
 255                 pthread_mutex_unlock(&wt->thread.lock);
 256
 257                 if (work)
 258                         seq = write_work(work);
 259         }
 260
 261         wt->thread.done = 1;
 262         pthread_cond_signal(&wt->thread.done_cond);
 263         return NULL;
 264 }
 265
 266 static void reader_work(struct work_item *work)
 267 {
 268         struct timeval s, e;
 269         ssize_t ret;
 270         size_t left;
 271         void *buf;
 272         off_t off;
 273
 274         gettimeofday(&s, NULL);
 275
 276         left = work->buf_size;
 277         buf = work->buf;
 278         off = work->off;
 279         while (left) {
 280                 ret = pread(work->fd, buf, left, off);
 281                 if (!ret) {
 282                         fprintf(stderr, "zero read\n");
 283                         break;
 284                 } else if (ret < 0) {
 285                         fprintf(stderr, "errno=%d\n", errno);
 286                         break;
 287                 }
 288                 left -= ret;
 289                 off += ret;
 290                 buf += ret;
 291         }
 292
 293         gettimeofday(&e, NULL);
 294
 295         add_lat(&work->reader->s, utime_since(&s, &e), "read");
 296
 297         pthread_cond_signal(&work->cond);
 298
 299         if (separate_writer) {
 300                 pthread_mutex_lock(&work->writer->thread.lock);
 301                 flist_add_tail(&work->list, &work->writer->list);
 302                 pthread_mutex_unlock(&work->writer->thread.lock);
 303                 pthread_cond_signal(&work->writer->thread.cond);
 304         } else {
 305                 struct reader_thread *rt = work->reader;
 306                 struct work_item *next = NULL;
 307                 struct flist_head *entry;
 308
 309                 /*
 310                  * Write current work if it matches in sequence.
 311                  */
 312                 if (work->seq == rt->write_seq)
 313                         goto write_it;
 314
 315                 pthread_mutex_lock(&rt->thread.lock);
 316
 317                 flist_add_tail(&work->list, &rt->done_list);
 318
 319                 /*
 320                  * See if the next work item is here, if so, write it
 321                  */
 322                 work = NULL;
 323                 flist_for_each(entry, &rt->done_list) {
 324                         next = flist_entry(entry, struct work_item, list);
 325                         if (next->seq == rt->write_seq) {
 326                                 work = next;
 327                                 flist_del(&work->list);
 328                                 break;
 329                         }
 330                 }
 331
 332                 pthread_mutex_unlock(&rt->thread.lock);
 333
 334                 if (work) {
 335 write_it:
 336                         write_work(work);
 337                         __sync_fetch_and_add(&rt->write_seq, 1);
 338                 }
 339         }
 340 }
 341
 342 static void *reader_one_off(void *data)
 343 {
 344         reader_work(data);
 345         return NULL;
 346 }
 347
 348 static void *reader_fn(void *data)
 349 {
 350         struct reader_thread *rt = data;
 351         struct work_item *work;
 352
 353         while (!rt->thread.exit || !flist_empty(&rt->list)) {
 354                 work = NULL;
 355                 pthread_mutex_lock(&rt->thread.lock);
 356                 if (!flist_empty(&rt->list)) {
 357                         work = flist_first_entry(&rt->list, struct work_item, list);
 358                         flist_del_init(&work->list);
 359                 } else
 360                         pthread_cond_wait(&rt->thread.cond, &rt->thread.lock);
 361                 pthread_mutex_unlock(&rt->thread.lock);
 362
 363                 if (work) {
 364                         rt->busy = 1;
 365                         reader_work(work);
 366                         rt->busy = 0;
 367                 }
 368         }
 369
 370         rt->thread.done = 1;
 371         pthread_cond_signal(&rt->thread.done_cond);
 372         return NULL;
 373 }
 374
 375 static void queue_work(struct reader_thread *rt, struct work_item *work)
 376 {
 377         if (!rt->started) {
 378                 pthread_mutex_lock(&rt->thread.lock);
 379                 flist_add_tail(&work->list, &rt->list);
 380                 pthread_mutex_unlock(&rt->thread.lock);
 381
 382                 rt->started = 1;
 383                 pthread_create(&rt->thread.thread, NULL, reader_fn, rt);
 384         } else if (!rt->busy && !pthread_mutex_trylock(&rt->thread.lock)) {
 385                 flist_add_tail(&work->list, &rt->list);
 386                 pthread_mutex_unlock(&rt->thread.lock);
 387
 388                 pthread_cond_signal(&rt->thread.cond);
 389         } else {
 390                 int ret = pthread_create(&work->thread, NULL, reader_one_off, work);
 391                 if (ret)
 392                         fprintf(stderr, "pthread_create=%d\n", ret);
 393                 else
 394                         pthread_detach(work->thread);
 395         }
 396 }
 397
 398 static unsigned int calc_percentiles(unsigned int *io_u_plat, unsigned long nr,
 399                                      unsigned int **output)
 400 {
 401         unsigned long sum = 0;
 402         unsigned int len, i, j = 0;
 403         unsigned int oval_len = 0;
 404         unsigned int *ovals = NULL;
 405         int is_last;
 406
 407         len = 0;
 408         while (len < PLAT_LIST_MAX && plist[len] != 0.0)
 409                 len++;
 410
 411         if (!len)
 412                 return 0;
 413
 414         /*
 415          * Calculate bucket values, note down max and min values
 416          */
 417         is_last = 0;
 418         for (i = 0; i < PLAT_NR && !is_last; i++) {
 419                 sum += io_u_plat[i];
 420                 while (sum >= (plist[j] / 100.0 * nr)) {
 421                         assert(plist[j] <= 100.0);
 422
 423                         if (j == oval_len) {
 424                                 oval_len += 100;
 425                                 ovals = realloc(ovals, oval_len * sizeof(unsigned int));
 426                         }
 427
 428                         ovals[j] = plat_idx_to_val(i);
 429                         is_last = (j == len - 1);
 430                         if (is_last)
 431                                 break;
 432
 433                         j++;
 434                 }
 435         }
 436
 437         *output = ovals;
 438         return len;
 439 }
 440
 441 static void show_latencies(struct stats *s, const char *msg)
 442 {
 443         unsigned int *ovals = NULL;
 444         unsigned int len, i;
 445
 446         len = calc_percentiles(s->plat, s->nr_samples, &ovals);
 447         if (len) {
 448                 fprintf(stderr, "Latency percentiles (usec) (%s)\n", msg);
 449                 for (i = 0; i < len; i++)
 450                         fprintf(stderr, "\t%2.4fth: %u\n", plist[i], ovals[i]);
 451         }
 452
 453         if (ovals)
 454                 free(ovals);
 455
 456         fprintf(stderr, "\tOver=%u, min=%u, max=%u\n", s->over, s->min, s->max);
 457 }
 458
 459 static void init_thread(struct thread_data *thread)
 460 {
 461         pthread_cond_init(&thread->cond, NULL);
 462         pthread_cond_init(&thread->done_cond, NULL);
 463         pthread_mutex_init(&thread->lock, NULL);
 464         pthread_mutex_init(&thread->done_lock, NULL);
 465         thread->exit = 0;
 466 }
 467
 468 static void exit_thread(struct thread_data *thread,
 469                         void fn(struct writer_thread *),
 470                         struct writer_thread *wt)
 471 {
 472         thread->exit = 1;
 473         pthread_cond_signal(&thread->cond);
 474
 475         while (!thread->done) {
 476                 pthread_mutex_lock(&thread->done_lock);
 477
 478                 if (fn) {
 479                         struct timespec t;
 480
 481                         clock_gettime(CLOCK_REALTIME, &t);
 482                         t.tv_sec++;
 483
 484
 485                         pthread_cond_timedwait(&thread->done_cond, &thread->done_lock, &t);
 486                         fn(wt);
 487                 } else
 488                         pthread_cond_wait(&thread->done_cond, &thread->done_lock);
 489
 490                 pthread_mutex_unlock(&thread->done_lock);
 491         }
 492 }
 493
 494 static int usage(char *argv[])
 495 {
 496         fprintf(stderr, "%s: [-b blocksize] [-t max usec] [-w separate writer] -f file\n", argv[0]);
 497         return 1;
 498 }
 499
 500 static int parse_options(int argc, char *argv[])
 501 {
 502         int c;
 503
 504         while ((c = getopt(argc, argv, "f:b:t:w:")) != -1) {
 505                 switch (c) {
 506                 case 'f':
 507                         file = strdup(optarg);
 508                         break;
 509                 case 'b':
 510                         bs = atoi(optarg);
 511                         break;
 512                 case 't':
 513                         max_us = atoi(optarg);
 514                         break;
 515                 case 'w':
 516                         separate_writer = atoi(optarg);
 517                         if (!separate_writer)
 518                                 fprintf(stderr, "inline writing is broken\n");
 519                         break;
 520                 case '?':
 521                 default:
 522                         return usage(argv);
 523                 }
 524         }
 525
 526         if (!file)
 527                 return usage(argv);
 528
 529         return 0;
 530 }
 531
 532 static void prune_done_entries(struct writer_thread *wt)
 533 {
 534         FLIST_HEAD(list);
 535
 536         if (flist_empty(&wt->done_list))
 537                 return;
 538
 539         if (pthread_mutex_trylock(&wt->thread.lock))
 540                 return;
 541
 542         if (!flist_empty(&wt->done_list))
 543                 flist_splice_init(&wt->done_list, &list);
 544         pthread_mutex_unlock(&wt->thread.lock);
 545
 546         while (!flist_empty(&list)) {
 547                 struct work_item *work;
 548
 549                 work = flist_first_entry(&list, struct work_item, list);
 550                 flist_del(&work->list);
 551
 552                 pthread_cond_destroy(&work->cond);
 553                 pthread_mutex_destroy(&work->lock);
 554                 free(work->buf);
 555                 free(work);
 556         }
 557 }
 558
 559 int main(int argc, char *argv[])
 560 {
 561         struct timeval s, re, we;
 562         struct reader_thread *rt;
 563         struct writer_thread *wt;
 564         unsigned long rate;
 565         struct stat sb;
 566         size_t bytes;
 567         off_t off;
 568         int fd, seq;
 569
 570         if (parse_options(argc, argv))
 571                 return 1;
 572
 573         fd = open(file, O_RDONLY);
 574         if (fd < 0) {
 575                 perror("open");
 576                 return 2;
 577         }
 578
 579         if (fstat(fd, &sb) < 0) {
 580                 perror("stat");
 581                 return 3;
 582         }
 583
 584         wt = &writer_thread;
 585         init_thread(&wt->thread);
 586         INIT_FLIST_HEAD(&wt->list);
 587         INIT_FLIST_HEAD(&wt->done_list);
 588         wt->s.max = 0;
 589         wt->s.min = -1U;
 590         pthread_create(&wt->thread.thread, NULL, writer_fn, wt);
 591
 592         rt = &reader_thread;
 593         init_thread(&rt->thread);
 594         INIT_FLIST_HEAD(&rt->list);
 595         INIT_FLIST_HEAD(&rt->done_list);
 596         rt->s.max = 0;
 597         rt->s.min = -1U;
 598         rt->write_seq = 1;
 599
 600         off = 0;
 601         seq = 0;
 602         bytes = 0;
 603
 604         gettimeofday(&s, NULL);
 605
 606         while (sb.st_size) {
 607                 struct work_item *work;
 608                 size_t this_len;
 609                 struct timespec t;
 610
 611                 prune_done_entries(wt);
 612
 613                 this_len = sb.st_size;
 614                 if (this_len > bs)
 615                         this_len = bs;
 616
 617                 work = calloc(1, sizeof(*work));
 618                 work->buf = malloc(this_len);
 619                 work->buf_size = this_len;
 620                 work->off = off;
 621                 work->fd = fd;
 622                 work->seq = ++seq;
 623                 work->writer = wt;
 624                 work->reader = rt;
 625                 pthread_cond_init(&work->cond, NULL);
 626                 pthread_mutex_init(&work->lock, NULL);
 627
 628                 queue_work(rt, work);
 629
 630                 clock_gettime(CLOCK_REALTIME, &t);
 631                 t.tv_nsec += max_us * 1000ULL;
 632                 if (t.tv_nsec >= 1000000000ULL) {
 633                         t.tv_nsec -= 1000000000ULL;
 634                         t.tv_sec++;
 635                 }
 636
 637                 pthread_mutex_lock(&work->lock);
 638                 pthread_cond_timedwait(&work->cond, &work->lock, &t);
 639                 pthread_mutex_unlock(&work->lock);
 640
 641                 off += this_len;
 642                 sb.st_size -= this_len;
 643                 bytes += this_len;
 644         }
 645
 646         exit_thread(&rt->thread, NULL, NULL);
 647         gettimeofday(&re, NULL);
 648
 649         exit_thread(&wt->thread, prune_done_entries, wt);
 650         gettimeofday(&we, NULL);
 651
 652         show_latencies(&rt->s, "READERS");
 653         show_latencies(&wt->s, "WRITERS");
 654
 655         bytes /= 1024;
 656         rate = (bytes * 1000UL * 1000UL) / utime_since(&s, &re);
 657         fprintf(stderr, "Read rate (KB/sec) : %lu\n", rate);
 658         rate = (bytes * 1000UL * 1000UL) / utime_since(&s, &we);
 659         fprintf(stderr, "Write rate (KB/sec): %lu\n", rate);
 660
 661         close(fd);
 662         return 0;
 663 }