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bcache: writeback rate shouldn't artifically clamp 

The previous code artificially limited writeback rate to 1000000
blocks/second (NSEC_PER_MSEC), which is a rate that can be met on fast
hardware.  The rate limiting code works fine (though with decreased
precision) up to 3 orders of magnitude faster, so use NSEC_PER_SEC.

Additionally, ensure that uint32_t is used as a type for rate throughout
the rate management so that type checking/clamp_t can work properly.

bch_next_delay should be rewritten for increased precision and better
handling of high rates and long sleep periods, but this is adequate for
now.

Signed-off-by: Michael Lyle <mlyle@lyle.org>
Reported-by: Coly Li <colyli@suse.de>
Reviewed-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Michael Lyle 2017-10-13 16:35:38 -07:00 committed by Jens Axboe
parent ae82ddbfeb
commit e41166c5c4
3 changed files with 7 additions and 6 deletions
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2
drivers/md/bcache/bcache.h
View File

@ -361,7 +361,7 @@ struct cached_dev {
int64_t writeback_rate_proportional; int64_t writeback_rate_proportional;
int64_t writeback_rate_integral; int64_t writeback_rate_integral;
int64_t writeback_rate_integral_scaled; int64_t writeback_rate_integral_scaled;
int64_t writeback_rate_change; int32_t writeback_rate_change;
unsigned writeback_rate_update_seconds; unsigned writeback_rate_update_seconds;
unsigned writeback_rate_i_term_inverse; unsigned writeback_rate_i_term_inverse;

4
drivers/md/bcache/util.h
View File

@ -441,10 +441,10 @@ struct bch_ratelimit {
uint64_t next; uint64_t next;
/* /*
* Rate at which we want to do work, in units per nanosecond * Rate at which we want to do work, in units per second
* The units here correspond to the units passed to bch_next_delay() * The units here correspond to the units passed to bch_next_delay()
*/ */
unsigned rate; uint32_t rate;
}; };
static inline void bch_ratelimit_reset(struct bch_ratelimit *d) static inline void bch_ratelimit_reset(struct bch_ratelimit *d)

7
drivers/md/bcache/writeback.c
View File

@ -52,7 +52,8 @@ static void __update_writeback_rate(struct cached_dev *dc)
int64_t error = dirty - target; int64_t error = dirty - target;
int64_t proportional_scaled = int64_t proportional_scaled =
div_s64(error, dc->writeback_rate_p_term_inverse); div_s64(error, dc->writeback_rate_p_term_inverse);
int64_t integral_scaled, new_rate; int64_t integral_scaled;
uint32_t new_rate;
if ((error < 0 && dc->writeback_rate_integral > 0) || if ((error < 0 && dc->writeback_rate_integral > 0) ||
(error > 0 && time_before64(local_clock(), (error > 0 && time_before64(local_clock(),
@ -74,8 +75,8 @@ static void __update_writeback_rate(struct cached_dev *dc)
integral_scaled = div_s64(dc->writeback_rate_integral, integral_scaled = div_s64(dc->writeback_rate_integral,
dc->writeback_rate_i_term_inverse); dc->writeback_rate_i_term_inverse);
new_rate = clamp_t(int64_t, (proportional_scaled + integral_scaled), new_rate = clamp_t(int32_t, (proportional_scaled + integral_scaled),
dc->writeback_rate_minimum, NSEC_PER_MSEC); dc->writeback_rate_minimum, NSEC_PER_SEC);
dc->writeback_rate_proportional = proportional_scaled; dc->writeback_rate_proportional = proportional_scaled;
dc->writeback_rate_integral_scaled = integral_scaled; dc->writeback_rate_integral_scaled = integral_scaled;