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-rw-r--r--drivers/md/bcache/bcache.h9
-rw-r--r--drivers/md/bcache/sysfs.c18
-rw-r--r--drivers/md/bcache/writeback.c91
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);
}
generated by cgit v1.2.3 (git 2.39.1) at 2024-12-13 08:46:55 +0000