On 2017/10/9 下午3:37, Michael Lyle wrote:
> 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@xxxxxxxx>
> Reported-by: Coly Li <colyli@xxxxxxx>
Current maximum rate number is around 488.2M/sec, it could be easily a
bottleneck for md raid0 deivce with SATA SSD or more hard drives. The
new maximum rate (476G/sec) should be enough for most of common hardware
configurations :-)
Reviewed-by: Coly Li <colyli@xxxxxxx>
Thanks.
Coly Li
> ---
> drivers/md/bcache/bcache.h | 2 +-
> drivers/md/bcache/util.h | 4 ++--
> drivers/md/bcache/writeback.c | 7 ++++---
> 3 files changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
> index df0b2ccfca8d..2f9c380c4692 100644
> --- a/drivers/md/bcache/bcache.h
> +++ b/drivers/md/bcache/bcache.h
> @@ -363,7 +363,7 @@ struct cached_dev {
> int64_t writeback_rate_proportional;
> int64_t writeback_rate_integral;
> int64_t writeback_rate_integral_scaled;
> - int64_t writeback_rate_change;
> + int32_t writeback_rate_change;
>
> unsigned writeback_rate_update_seconds;
> unsigned writeback_rate_i_term_inverse;
> diff --git a/drivers/md/bcache/util.h b/drivers/md/bcache/util.h
> index cb8d2ccbb6c6..8f509290bb02 100644
> --- a/drivers/md/bcache/util.h
> +++ b/drivers/md/bcache/util.h
> @@ -441,10 +441,10 @@ struct bch_ratelimit {
> 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()
> */
> - unsigned rate;
> + uint32_t rate;
> };
>
> static inline void bch_ratelimit_reset(struct bch_ratelimit *d)
> diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c
> index d63356a60001..42d087b9fb56 100644
> --- a/drivers/md/bcache/writeback.c
> +++ b/drivers/md/bcache/writeback.c
> @@ -52,7 +52,8 @@ static void __update_writeback_rate(struct cached_dev *dc)
> int64_t error = dirty - target;
> int64_t proportional_scaled =
> 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) ||
> (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,
> dc->writeback_rate_i_term_inverse);
>
> - new_rate = clamp_t(int64_t, (proportional_scaled + integral_scaled),
> - dc->writeback_rate_minimum, NSEC_PER_MSEC);
> + new_rate = clamp_t(int32_t, (proportional_scaled + integral_scaled),
> + dc->writeback_rate_minimum, NSEC_PER_SEC);
>
> dc->writeback_rate_proportional = proportional_scaled;
> dc->writeback_rate_integral_scaled = integral_scaled;
