diff options
| author | Michael Lyle <mlyle@lyle.org> | 2017-10-13 16:35:36 -0700 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2017-10-16 09:07:26 -0600 |
| commit | 1d316e658374f700fdfff9299c70ce65d8d145e6 (patch) | |
| tree | 38b763dc0480f4fa972e69ca06793d1a2f9c670c /drivers/md/bcache/bcache.h | |
| parent | 5fa89fb9a86bcc0f0b3f21ab6087a8a4170dcd2c (diff) | |
bcache: implement PI controller for writeback rate
bcache uses a control system to attempt to keep the amount of dirty data
in cache at a user-configured level, while not responding excessively to
transients and variations in write rate. Previously, the system was a
PD controller; but the output from it was integrated, turning the
Proportional term into an Integral term, and turning the Derivative term
into a crude Proportional term. Performance of the controller has been
uneven in production, and it has tended to respond slowly, oscillate,
and overshoot.
This patch set replaces the current control system with an explicit PI
controller and tuning that should be correct for most hardware. By
default, it attempts to write at a rate that would retire 1/40th of the
current excess blocks per second. An integral term in turn works to
remove steady state errors.
IMO, this yields benefits in simplicity (removing weighted average
filtering, etc) and system performance.
Another small change is a tunable parameter is introduced to allow the
user to specify a minimum rate at which dirty blocks are retired.
There is a slight difference from earlier versions of the patch in
integral handling to prevent excessive negative integral windup.
Signed-off-by: Michael Lyle <mlyle@lyle.org>
Reviewed-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'drivers/md/bcache/bcache.h')
| -rw-r--r-- | drivers/md/bcache/bcache.h | 9 |
1 files changed, 4 insertions, 5 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 { |