diff options
Diffstat (limited to 'drivers')
-rw-r--r-- | drivers/md/bcache/bcache.h | 9 | ||||
-rw-r--r-- | drivers/md/bcache/sysfs.c | 18 | ||||
-rw-r--r-- | drivers/md/bcache/writeback.c | 91 |
3 files changed, 66 insertions, 52 deletions
diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h index 2ed9bd231d84..eb83be693d60 100644 --- a/drivers/md/bcache/bcache.h +++ b/drivers/md/bcache/bcache.h @@ -265,9 +265,6 @@ struct bcache_device { atomic_t *stripe_sectors_dirty; unsigned long *full_dirty_stripes; - unsigned long sectors_dirty_last; - long sectors_dirty_derivative; - struct bio_set *bio_split; unsigned data_csum:1; @@ -362,12 +359,14 @@ struct cached_dev { uint64_t writeback_rate_target; int64_t writeback_rate_proportional; - int64_t writeback_rate_derivative; + int64_t writeback_rate_integral; + int64_t writeback_rate_integral_scaled; int64_t writeback_rate_change; unsigned writeback_rate_update_seconds; - unsigned writeback_rate_d_term; + unsigned writeback_rate_i_term_inverse; unsigned writeback_rate_p_term_inverse; + unsigned writeback_rate_minimum; }; enum alloc_reserve { diff --git a/drivers/md/bcache/sysfs.c b/drivers/md/bcache/sysfs.c index 69f355b9650c..2290bffd4922 100644 --- a/drivers/md/bcache/sysfs.c +++ b/drivers/md/bcache/sysfs.c @@ -81,8 +81,9 @@ rw_attribute(writeback_delay); rw_attribute(writeback_rate); rw_attribute(writeback_rate_update_seconds); -rw_attribute(writeback_rate_d_term); +rw_attribute(writeback_rate_i_term_inverse); rw_attribute(writeback_rate_p_term_inverse); +rw_attribute(writeback_rate_minimum); read_attribute(writeback_rate_debug); read_attribute(stripe_size); @@ -130,15 +131,16 @@ SHOW(__bch_cached_dev) sysfs_hprint(writeback_rate, dc->writeback_rate.rate << 9); var_print(writeback_rate_update_seconds); - var_print(writeback_rate_d_term); + var_print(writeback_rate_i_term_inverse); var_print(writeback_rate_p_term_inverse); + var_print(writeback_rate_minimum); if (attr == &sysfs_writeback_rate_debug) { char rate[20]; char dirty[20]; char target[20]; char proportional[20]; - char derivative[20]; + char integral[20]; char change[20]; s64 next_io; @@ -146,7 +148,7 @@ SHOW(__bch_cached_dev) bch_hprint(dirty, bcache_dev_sectors_dirty(&dc->disk) << 9); bch_hprint(target, dc->writeback_rate_target << 9); bch_hprint(proportional,dc->writeback_rate_proportional << 9); - bch_hprint(derivative, dc->writeback_rate_derivative << 9); + bch_hprint(integral, dc->writeback_rate_integral_scaled << 9); bch_hprint(change, dc->writeback_rate_change << 9); next_io = div64_s64(dc->writeback_rate.next - local_clock(), @@ -157,11 +159,11 @@ SHOW(__bch_cached_dev) "dirty:\t\t%s\n" "target:\t\t%s\n" "proportional:\t%s\n" - "derivative:\t%s\n" + "integral:\t%s\n" "change:\t\t%s/sec\n" "next io:\t%llims\n", rate, dirty, target, proportional, - derivative, change, next_io); + integral, change, next_io); } sysfs_hprint(dirty_data, @@ -213,7 +215,7 @@ STORE(__cached_dev) dc->writeback_rate.rate, 1, INT_MAX); d_strtoul_nonzero(writeback_rate_update_seconds); - d_strtoul(writeback_rate_d_term); + d_strtoul(writeback_rate_i_term_inverse); d_strtoul_nonzero(writeback_rate_p_term_inverse); d_strtoi_h(sequential_cutoff); @@ -319,7 +321,7 @@ static struct attribute *bch_cached_dev_files[] = { &sysfs_writeback_percent, &sysfs_writeback_rate, &sysfs_writeback_rate_update_seconds, - &sysfs_writeback_rate_d_term, + &sysfs_writeback_rate_i_term_inverse, &sysfs_writeback_rate_p_term_inverse, &sysfs_writeback_rate_debug, &sysfs_dirty_data, diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c index 5e65a392287d..cac8678da5d0 100644 --- a/drivers/md/bcache/writeback.c +++ b/drivers/md/bcache/writeback.c @@ -25,48 +25,62 @@ static void __update_writeback_rate(struct cached_dev *dc) bcache_flash_devs_sectors_dirty(c); uint64_t cache_dirty_target = div_u64(cache_sectors * dc->writeback_percent, 100); - int64_t target = div64_u64(cache_dirty_target * bdev_sectors(dc->bdev), c->cached_dev_sectors); - /* PD controller */ - + /* + * PI controller: + * Figures out the amount that should be written per second. + * + * First, the error (number of sectors that are dirty beyond our + * target) is calculated. The error is accumulated (numerically + * integrated). + * + * Then, the proportional value and integral value are scaled + * based on configured values. These are stored as inverses to + * avoid fixed point math and to make configuration easy-- e.g. + * the default value of 40 for writeback_rate_p_term_inverse + * attempts to write at a rate that would retire all the dirty + * blocks in 40 seconds. + * + * The writeback_rate_i_inverse value of 10000 means that 1/10000th + * of the error is accumulated in the integral term per second. + * This acts as a slow, long-term average that is not subject to + * variations in usage like the p term. + */ int64_t dirty = bcache_dev_sectors_dirty(&dc->disk); - int64_t derivative = dirty - dc->disk.sectors_dirty_last; - int64_t proportional = dirty - target; - int64_t change; - - dc->disk.sectors_dirty_last = dirty; - - /* Scale to sectors per second */ - - proportional *= dc->writeback_rate_update_seconds; - proportional = div_s64(proportional, dc->writeback_rate_p_term_inverse); - - derivative = div_s64(derivative, dc->writeback_rate_update_seconds); - - derivative = ewma_add(dc->disk.sectors_dirty_derivative, derivative, - (dc->writeback_rate_d_term / - dc->writeback_rate_update_seconds) ?: 1, 0); - - derivative *= dc->writeback_rate_d_term; - derivative = div_s64(derivative, dc->writeback_rate_p_term_inverse); - - change = proportional + derivative; + int64_t error = dirty - target; + int64_t proportional_scaled = + div_s64(error, dc->writeback_rate_p_term_inverse); + int64_t integral_scaled, new_rate; + + if ((error < 0 && dc->writeback_rate_integral > 0) || + (error > 0 && time_before64(local_clock(), + dc->writeback_rate.next + NSEC_PER_MSEC))) { + /* + * Only decrease the integral term if it's more than + * zero. Only increase the integral term if the device + * is keeping up. (Don't wind up the integral + * ineffectively in either case). + * + * It's necessary to scale this by + * writeback_rate_update_seconds to keep the integral + * term dimensioned properly. + */ + dc->writeback_rate_integral += error * + dc->writeback_rate_update_seconds; + } - /* Don't increase writeback rate if the device isn't keeping up */ - if (change > 0 && - time_after64(local_clock(), - dc->writeback_rate.next + NSEC_PER_MSEC)) - change = 0; + integral_scaled = div_s64(dc->writeback_rate_integral, + dc->writeback_rate_i_term_inverse); - dc->writeback_rate.rate = - clamp_t(int64_t, (int64_t) dc->writeback_rate.rate + change, - 1, NSEC_PER_MSEC); + new_rate = clamp_t(int64_t, (proportional_scaled + integral_scaled), + dc->writeback_rate_minimum, NSEC_PER_MSEC); - dc->writeback_rate_proportional = proportional; - dc->writeback_rate_derivative = derivative; - dc->writeback_rate_change = change; + dc->writeback_rate_proportional = proportional_scaled; + dc->writeback_rate_integral_scaled = integral_scaled; + dc->writeback_rate_change = new_rate - dc->writeback_rate.rate; + dc->writeback_rate.rate = new_rate; dc->writeback_rate_target = target; } @@ -499,8 +513,6 @@ void bch_sectors_dirty_init(struct bcache_device *d) bch_btree_map_keys(&op.op, d->c, &KEY(op.inode, 0, 0), sectors_dirty_init_fn, 0); - - d->sectors_dirty_last = bcache_dev_sectors_dirty(d); } void bch_cached_dev_writeback_init(struct cached_dev *dc) @@ -514,10 +526,11 @@ void bch_cached_dev_writeback_init(struct cached_dev *dc) dc->writeback_percent = 10; dc->writeback_delay = 30; dc->writeback_rate.rate = 1024; + dc->writeback_rate_minimum = 1; dc->writeback_rate_update_seconds = 5; - dc->writeback_rate_d_term = 30; - dc->writeback_rate_p_term_inverse = 6000; + dc->writeback_rate_p_term_inverse = 40; + dc->writeback_rate_i_term_inverse = 10000; INIT_DELAYED_WORK(&dc->writeback_rate_update, update_writeback_rate); } |