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.
11 * $ time (./read-to-pipe-async -f randfile.gz | gzip -dc > outfile; sync)
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
18 * gcc -Wall -g -O2 -o read-to-pipe-async read-to-pipe-async.c -lpthread
20 * Copyright (C) 2016 Jens Axboe
29 #include <sys/types.h>
40 static int max_us = 10000;
42 static int separate_writer = 1;
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
51 unsigned int plat[PLAT_NR];
52 unsigned int nr_samples;
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, };
65 pthread_mutex_t done_lock;
66 pthread_cond_t done_cond;
70 struct writer_thread {
71 struct flist_head list;
72 struct flist_head done_list;
74 struct thread_data thread;
77 struct reader_thread {
78 struct flist_head list;
79 struct flist_head done_list;
84 struct thread_data thread;
88 struct flist_head list;
94 struct writer_thread *writer;
95 struct reader_thread *reader;
101 static struct reader_thread reader_thread;
102 static struct writer_thread writer_thread;
104 uint64_t utime_since(const struct timespec *s, const struct timespec *e)
109 sec = e->tv_sec - s->tv_sec;
110 usec = (e->tv_nsec - s->tv_nsec) / 1000;
111 if (sec > 0 && usec < 0) {
116 if (sec < 0 || (sec == 0 && usec < 0))
119 ret = sec * 1000000ULL + usec;
124 static struct work_item *find_seq(struct writer_thread *w, unsigned int seq)
126 struct work_item *work;
127 struct flist_head *entry;
129 if (flist_empty(&w->list))
132 flist_for_each(entry, &w->list) {
133 work = flist_entry(entry, struct work_item, list);
134 if (work->seq == seq)
141 static unsigned int plat_val_to_idx(unsigned int val)
143 unsigned int msb, error_bits, base, offset;
145 /* Find MSB starting from bit 0 */
149 msb = sizeof(val)*8 - __builtin_clz(val) - 1;
152 * MSB <= (PLAT_BITS-1), cannot be rounded off. Use
153 * all bits of the sample as index
155 if (msb <= PLAT_BITS)
158 /* Compute the number of error bits to discard*/
159 error_bits = msb - PLAT_BITS;
161 /* Compute the number of buckets before the group */
162 base = (error_bits + 1) << PLAT_BITS;
165 * Discard the error bits and apply the mask to find the
166 * index for the buckets in the group
168 offset = (PLAT_VAL - 1) & (val >> error_bits);
170 /* Make sure the index does not exceed (array size - 1) */
171 return (base + offset) < (PLAT_NR - 1) ?
172 (base + offset) : (PLAT_NR - 1);
176 * Convert the given index of the bucket array to the value
177 * represented by the bucket
179 static unsigned int plat_idx_to_val(unsigned int idx)
181 unsigned int error_bits, k, base;
183 assert(idx < PLAT_NR);
185 /* MSB <= (PLAT_BITS-1), cannot be rounded off. Use
186 * all bits of the sample as index */
187 if (idx < (PLAT_VAL << 1))
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);
194 /* Find its bucket number of the group */
197 /* Return the mean of the range of the bucket */
198 return base + ((k + 0.5) * (1 << error_bits));
201 static void add_lat(struct stats *s, unsigned int us, const char *name)
211 fprintf(stderr, "%s latency=%u usec\n", name, us);
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);
220 static int write_work(struct work_item *work)
222 struct timespec s, e;
225 clock_gettime(CLOCK_MONOTONIC, &s);
226 ret = write(STDOUT_FILENO, work->buf, work->buf_size);
227 clock_gettime(CLOCK_MONOTONIC, &e);
228 assert(ret == work->buf_size);
230 add_lat(&work->writer->s, utime_since(&s, &e), "write");
231 return work->seq + 1;
234 static void thread_exiting(struct thread_data *thread)
236 __sync_fetch_and_add(&thread->done, 1);
237 pthread_cond_signal(&thread->done_cond);
240 static void *writer_fn(void *data)
242 struct writer_thread *wt = data;
243 struct work_item *work;
244 unsigned int seq = 1;
247 while (!wt->thread.exit || !flist_empty(&wt->list)) {
248 pthread_mutex_lock(&wt->thread.lock);
251 flist_add_tail(&work->list, &wt->done_list);
253 work = find_seq(wt, seq);
255 flist_del_init(&work->list);
257 pthread_cond_wait(&wt->thread.cond, &wt->thread.lock);
259 pthread_mutex_unlock(&wt->thread.lock);
262 seq = write_work(work);
265 thread_exiting(&wt->thread);
269 static void reader_work(struct work_item *work)
271 struct timespec s, e;
277 clock_gettime(CLOCK_MONOTONIC, &s);
279 left = work->buf_size;
283 ret = pread(work->fd, buf, left, off);
285 fprintf(stderr, "zero read\n");
287 } else if (ret < 0) {
288 fprintf(stderr, "errno=%d\n", errno);
296 clock_gettime(CLOCK_MONOTONIC, &e);
298 add_lat(&work->reader->s, utime_since(&s, &e), "read");
300 pthread_cond_signal(&work->cond);
302 if (separate_writer) {
303 pthread_mutex_lock(&work->writer->thread.lock);
304 flist_add_tail(&work->list, &work->writer->list);
305 pthread_mutex_unlock(&work->writer->thread.lock);
306 pthread_cond_signal(&work->writer->thread.cond);
308 struct reader_thread *rt = work->reader;
309 struct work_item *next = NULL;
310 struct flist_head *entry;
313 * Write current work if it matches in sequence.
315 if (work->seq == rt->write_seq)
318 pthread_mutex_lock(&rt->thread.lock);
320 flist_add_tail(&work->list, &rt->done_list);
323 * See if the next work item is here, if so, write it
326 flist_for_each(entry, &rt->done_list) {
327 next = flist_entry(entry, struct work_item, list);
328 if (next->seq == rt->write_seq) {
330 flist_del(&work->list);
335 pthread_mutex_unlock(&rt->thread.lock);
340 __sync_fetch_and_add(&rt->write_seq, 1);
345 static void *reader_one_off(void *data)
351 static void *reader_fn(void *data)
353 struct reader_thread *rt = data;
354 struct work_item *work;
356 while (!rt->thread.exit || !flist_empty(&rt->list)) {
358 pthread_mutex_lock(&rt->thread.lock);
359 if (!flist_empty(&rt->list)) {
360 work = flist_first_entry(&rt->list, struct work_item, list);
361 flist_del_init(&work->list);
363 pthread_cond_wait(&rt->thread.cond, &rt->thread.lock);
364 pthread_mutex_unlock(&rt->thread.lock);
367 __sync_fetch_and_add(&rt->busy, 1);
369 __sync_fetch_and_sub(&rt->busy, 1);
373 thread_exiting(&rt->thread);
377 static void queue_work(struct reader_thread *rt, struct work_item *work)
380 pthread_mutex_lock(&rt->thread.lock);
381 flist_add_tail(&work->list, &rt->list);
382 pthread_mutex_unlock(&rt->thread.lock);
385 pthread_create(&rt->thread.thread, NULL, reader_fn, rt);
386 } else if (!rt->busy && !pthread_mutex_trylock(&rt->thread.lock)) {
387 flist_add_tail(&work->list, &rt->list);
388 pthread_mutex_unlock(&rt->thread.lock);
390 pthread_cond_signal(&rt->thread.cond);
392 int ret = pthread_create(&work->thread, NULL, reader_one_off, work);
394 fprintf(stderr, "pthread_create=%d\n", ret);
396 ret = pthread_detach(work->thread);
398 fprintf(stderr, "pthread_detach=%d\n", ret);
403 static unsigned int calc_percentiles(unsigned int *io_u_plat, unsigned long nr,
404 unsigned int **output)
406 unsigned long sum = 0;
407 unsigned int len, i, j = 0;
408 unsigned int oval_len = 0;
409 unsigned int *ovals = NULL;
413 while (len < PLAT_LIST_MAX && plist[len] != 0.0)
420 * Calculate bucket values, note down max and min values
423 for (i = 0; i < PLAT_NR && !is_last; i++) {
425 while (sum >= (plist[j] / 100.0 * nr)) {
426 assert(plist[j] <= 100.0);
430 ovals = realloc(ovals, oval_len * sizeof(unsigned int));
433 ovals[j] = plat_idx_to_val(i);
434 is_last = (j == len - 1);
446 static void show_latencies(struct stats *s, const char *msg)
448 unsigned int *ovals = NULL;
451 len = calc_percentiles(s->plat, s->nr_samples, &ovals);
453 fprintf(stderr, "Latency percentiles (usec) (%s)\n", msg);
454 for (i = 0; i < len; i++)
455 fprintf(stderr, "\t%2.4fth: %u\n", plist[i], ovals[i]);
461 fprintf(stderr, "\tOver=%u, min=%u, max=%u\n", s->over, s->min, s->max);
464 static void init_thread(struct thread_data *thread)
466 pthread_condattr_t cattr;
469 ret = pthread_condattr_init(&cattr);
471 #ifdef CONFIG_PTHREAD_CONDATTR_SETCLOCK
472 ret = pthread_condattr_setclock(&cattr, CLOCK_MONOTONIC);
475 pthread_cond_init(&thread->cond, &cattr);
476 pthread_cond_init(&thread->done_cond, &cattr);
477 pthread_mutex_init(&thread->lock, NULL);
478 pthread_mutex_init(&thread->done_lock, NULL);
482 static void exit_thread(struct thread_data *thread,
483 void fn(struct writer_thread *),
484 struct writer_thread *wt)
486 __sync_fetch_and_add(&thread->exit, 1);
487 pthread_cond_signal(&thread->cond);
489 while (!thread->done) {
490 pthread_mutex_lock(&thread->done_lock);
495 #ifdef CONFIG_PTHREAD_CONDATTR_SETCLOCK
496 clock_gettime(CLOCK_MONOTONIC, &ts);
498 clock_gettime(CLOCK_REALTIME, &ts);
502 pthread_cond_timedwait(&thread->done_cond, &thread->done_lock, &ts);
505 pthread_cond_wait(&thread->done_cond, &thread->done_lock);
507 pthread_mutex_unlock(&thread->done_lock);
511 static int usage(char *argv[])
513 fprintf(stderr, "%s: [-b blocksize] [-t max usec] [-w separate writer] -f file\n", argv[0]);
517 static int parse_options(int argc, char *argv[])
521 while ((c = getopt(argc, argv, "f:b:t:w:")) != -1) {
526 file = strdup(optarg);
532 max_us = atoi(optarg);
535 separate_writer = atoi(optarg);
536 if (!separate_writer)
537 fprintf(stderr, "inline writing is broken\n");
551 static void prune_done_entries(struct writer_thread *wt)
555 if (flist_empty(&wt->done_list))
558 if (pthread_mutex_trylock(&wt->thread.lock))
561 if (!flist_empty(&wt->done_list))
562 flist_splice_init(&wt->done_list, &list);
563 pthread_mutex_unlock(&wt->thread.lock);
565 while (!flist_empty(&list)) {
566 struct work_item *work;
568 work = flist_first_entry(&list, struct work_item, list);
569 flist_del(&work->list);
571 pthread_cond_destroy(&work->cond);
572 pthread_mutex_destroy(&work->lock);
578 int main(int argc, char *argv[])
580 pthread_condattr_t cattr;
581 struct timespec s, re, we;
582 struct reader_thread *rt;
583 struct writer_thread *wt;
592 if (parse_options(argc, argv))
595 fd = open(file, O_RDONLY);
601 if (fstat(fd, &sb) < 0) {
607 init_thread(&wt->thread);
608 INIT_FLIST_HEAD(&wt->list);
609 INIT_FLIST_HEAD(&wt->done_list);
612 pthread_create(&wt->thread.thread, NULL, writer_fn, wt);
615 init_thread(&rt->thread);
616 INIT_FLIST_HEAD(&rt->list);
617 INIT_FLIST_HEAD(&rt->done_list);
626 ret = pthread_condattr_init(&cattr);
628 #ifdef CONFIG_PTHREAD_CONDATTR_SETCLOCK
629 ret = pthread_condattr_setclock(&cattr, CLOCK_MONOTONIC);
633 clock_gettime(CLOCK_MONOTONIC, &s);
636 struct work_item *work;
640 prune_done_entries(wt);
642 this_len = sb.st_size;
646 work = calloc(1, sizeof(*work));
647 work->buf = malloc(this_len);
648 work->buf_size = this_len;
654 pthread_cond_init(&work->cond, &cattr);
655 pthread_mutex_init(&work->lock, NULL);
657 queue_work(rt, work);
659 #ifdef CONFIG_PTHREAD_CONDATTR_SETCLOCK
660 clock_gettime(CLOCK_MONOTONIC, &ts);
662 clock_gettime(CLOCK_REALTIME, &ts);
664 ts.tv_nsec += max_us * 1000ULL;
665 if (ts.tv_nsec >= 1000000000ULL) {
666 ts.tv_nsec -= 1000000000ULL;
670 pthread_mutex_lock(&work->lock);
671 pthread_cond_timedwait(&work->cond, &work->lock, &ts);
672 pthread_mutex_unlock(&work->lock);
675 sb.st_size -= this_len;
679 exit_thread(&rt->thread, NULL, NULL);
680 clock_gettime(CLOCK_MONOTONIC, &re);
682 exit_thread(&wt->thread, prune_done_entries, wt);
683 clock_gettime(CLOCK_MONOTONIC, &we);
685 show_latencies(&rt->s, "READERS");
686 show_latencies(&wt->s, "WRITERS");
689 elapsed = utime_since(&s, &re);
690 rate = elapsed ? (bytes * 1000UL * 1000UL) / elapsed : 0;
691 fprintf(stderr, "Read rate (KiB/sec) : %lu\n", rate);
692 elapsed = utime_since(&s, &we);
693 rate = elapsed ? (bytes * 1000UL * 1000UL) / elapsed : 0;
694 fprintf(stderr, "Write rate (KiB/sec): %lu\n", rate);