From: ZouMingzhe <mingzhe.zou@xxxxxxxxxxxx>
The writeback_rate value can be dynamically modified by PI controller.
However, the PI is only valid when dirty > target and writeback_rate
will be limited to writeback_rate_minimum when dirty < target.
The target value is calculated by __calc_target_rate() and user can
modify write_percent to change target. The write_percent can be any
integer between 0 and bch_cutoff_writeback, but 0 is a special value.
If the write_percent is 0, the writeback_rate will never update.
If we want to self-adaptive adjustment writeback_rate when dirty > 0,
this is impossible! This patch add writeback_dynamic_rate in configfs
to replace the logic of write_percent = 0. Then, the write_percent can
be set to 0 if we hope the PI controller to work consistently.
Below is the performance data under 300G caching disk and 100G backing disk.
For same parameters (use default value):
writeback_rate_minimum : 8 (4k/s)
writeback_rate_p_term_inverse : 40
writeback_rate_i_term_inverse : 10000
writeback_rate_update_seconds : 5
For different parameters:
A. enable dynamic rate and keep 1% dirty_data (writeback target abort 3G)
writeback_dynamic_rate = 1, writeback_percent = 1
B. enable dynamic rate and keep 0% dirty_data
writeback_dynamic_rate = 1, writeback_percent = 0
C. disable dynamic rate
writeback_dynamic_rate = 0
Test results:
Tab.1 fio randwrite 10GiB under rate 100MiB/s
================================================================
time | 10s | 20s | 30s | 40s | 50s | 60s
--------------+-------+-------+-------+-------+-------+---------
A's dirty | 0.9G | 1.9G | 2.9G | 3.5G | 4.7G | 5.5G
rate(p+i) | 4k | 4k | 6.2M | 18.4M | 43.0M | 65.7M
rate_p |-55.5M |-29.9M |-4.3M | 7.6M | 32.3M | 55.0M
rate_i | 12.4M | 11.0M | 10.5M | 10.7M | 10.7M | 10.7M
--------------+-------+-------+-------+-------+-------+---------
B's dirty | 958.2M| 1.7G | 2.6G | 3.4G | 4.3G | 5.2G
rate(p+i) | 38.4M | 60.6M | 71.9M | 94.1M | 117.1M| 139.5M
rate_p | 23.2M | 45.4M | 56.7M | 78.9M | 102.0M| 124.4M
rate_i | 15.1M | 15.1M | 15.1M | 15.1M | 15.1M | 15.1M
--------------+-------+-------+-------+-------+-------+---------
C's dirty | 931.9M| 1.7G | 2.6G | 3.4G | 4.3G | 5.1G
rate(p+i) | N/A | N/A | N/A | N/A | N/A | N/A
================================================================
Tab.2 fio randwrite 10GiB under rate 10MiB/s
================================================================
time | 100s | 200s | 300s | 400s | 500s | 600s
--------------+-------+-------+-------+-------+-------+---------
A's dirty | 0.9G | 1.9G | 2.9G | 3.4G | 3.4G | 3.3G
rate(p+i) | 4k | 4k | 4k | 9.2M | 10.6M | 10.7M
rate_p |-55.5M |-29.9M |-4.3M | 9.1M | 8.5M | 6.7M
rate_i |-1.1M |-1.1M |-1.1M | 123.5k| 2.1M | 3.9M
--------------+-------+-------+-------+-------+-------+---------
B's dirty | 134.6M| 94.5M | 109.1M| 78.6M | 65.0M | 69.9M
rate(p+i) | 11.7M | 11.1M | 11.6M | 11.3M | 11.2M | 11.6M
rate_p | 3.6M | 2.4M | 2.7M | 2.1M | 1.6M | 1.7M
rate_i | 8.1M | 8.6M | 8.9M | 9.2M | 9.6M | 9.8M
--------------+-------+-------+-------+-------+-------+---------
C's dirty | 56.1M | 30.6M | 19.0M | 16.9M | 14.5M | 22.5M
rate(p+i) | N/A | N/A | N/A | N/A | N/A | N/A
================================================================
Signed-off-by: Mingzhe Zou <mingzhe.zou@xxxxxxxxxxxx>
---
drivers/md/bcache/bcache.h | 1 +
drivers/md/bcache/sysfs.c | 5 +++++
drivers/md/bcache/writeback.c | 7 ++++---
3 files changed, 10 insertions(+), 3 deletions(-)
diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
index 9ed9c955add7..752f23c5c3c5 100644
--- a/drivers/md/bcache/bcache.h
+++ b/drivers/md/bcache/bcache.h
@@ -372,6 +372,7 @@ struct cached_dev {
unsigned int partial_stripes_expensive:1;
unsigned int writeback_metadata:1;
unsigned int writeback_running:1;
+ unsigned int writeback_dynamic_rate:1;
unsigned int writeback_consider_fragment:1;
unsigned char writeback_percent;
unsigned int writeback_delay;
diff --git a/drivers/md/bcache/sysfs.c b/drivers/md/bcache/sysfs.c
index 1f0dce30fa75..d251ce0d259f 100644
--- a/drivers/md/bcache/sysfs.c
+++ b/drivers/md/bcache/sysfs.c
@@ -117,6 +117,7 @@ rw_attribute(writeback_running);
rw_attribute(writeback_percent);
rw_attribute(writeback_delay);
rw_attribute(writeback_rate);
+rw_attribute(writeback_dynamic_rate);
rw_attribute(writeback_consider_fragment);
rw_attribute(writeback_rate_update_seconds);
@@ -198,6 +199,7 @@ SHOW(__bch_cached_dev)
var_printf(bypass_torture_test, "%i");
var_printf(writeback_metadata, "%i");
var_printf(writeback_running, "%i");
+ var_printf(writeback_dynamic_rate, "%i");
var_printf(writeback_consider_fragment, "%i");
var_print(writeback_delay);
var_print(writeback_percent);
@@ -309,6 +311,7 @@ STORE(__cached_dev)
sysfs_strtoul_bool(bypass_torture_test, dc->bypass_torture_test);
sysfs_strtoul_bool(writeback_metadata, dc->writeback_metadata);
sysfs_strtoul_bool(writeback_running, dc->writeback_running);
+ sysfs_strtoul_bool(writeback_dynamic_rate, dc->writeback_dynamic_rate);
sysfs_strtoul_bool(writeback_consider_fragment, dc->writeback_consider_fragment);
sysfs_strtoul_clamp(writeback_delay, dc->writeback_delay, 0, UINT_MAX);
@@ -329,6 +332,7 @@ STORE(__cached_dev)
return ret;
}
+
sysfs_strtoul_clamp(writeback_rate_update_seconds,
dc->writeback_rate_update_seconds,
1, WRITEBACK_RATE_UPDATE_SECS_MAX);
@@ -515,6 +519,7 @@ static struct attribute *bch_cached_dev_files[] = {
&sysfs_writeback_delay,
&sysfs_writeback_percent,
&sysfs_writeback_rate,
+ &sysfs_writeback_dynamic_rate,
&sysfs_writeback_consider_fragment,
&sysfs_writeback_rate_update_seconds,
&sysfs_writeback_rate_i_term_inverse,
diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c
index c7560f66dca8..45150881146e 100644
--- a/drivers/md/bcache/writeback.c
+++ b/drivers/md/bcache/writeback.c
@@ -235,7 +235,7 @@ static void update_writeback_rate(struct work_struct *work)
return;
}
- if (atomic_read(&dc->has_dirty) && dc->writeback_percent) {
+ if (atomic_read(&dc->has_dirty) && dc->writeback_dynamic_rate) {
/*
* If the whole cache set is idle, set_at_max_writeback_rate()
* will set writeback rate to a max number. Then it is
@@ -274,7 +274,7 @@ static unsigned int writeback_delay(struct cached_dev *dc,
unsigned int sectors)
{
if (test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags) ||
- !dc->writeback_percent)
+ !dc->writeback_dynamic_rate)
return 0;
return bch_next_delay(&dc->writeback_rate, sectors);
@@ -294,7 +294,7 @@ static void dirty_init(struct keybuf_key *w)
bio_init(bio, bio->bi_inline_vecs,
DIV_ROUND_UP(KEY_SIZE(&w->key), PAGE_SECTORS));
- if (!io->dc->writeback_percent)
+ if (!io->dc->writeback_dynamic_rate)
bio_set_prio(bio, IOPRIO_PRIO_VALUE(IOPRIO_CLASS_IDLE, 0));
bio->bi_iter.bi_size = KEY_SIZE(&w->key) << 9;
@@ -1014,6 +1014,7 @@ void bch_cached_dev_writeback_init(struct cached_dev *dc)
dc->writeback_metadata = true;
dc->writeback_running = false;
+ dc->writeback_dynamic_rate = true;
dc->writeback_consider_fragment = true;
dc->writeback_percent = 10;
dc->writeback_delay = 30;
--
2.17.1
