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>

diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
index eb83be6..d77c482 100644 (file)
--- a/drivers/md/bcache/bcache.h
+++ b/drivers/md/bcache/bcache.h
@@ -361,7 +361,7 @@ 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 cb8d2cc..8f50929 100644 (file)
--- 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 8deb721..897d280 100644 (file)
--- 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;