From 16749c23c00c686ed168471963e3ddb0f3fcd855 Mon Sep 17 00:00:00 2001 From: Kent Overstreet Date: Mon, 11 Nov 2013 13:58:34 -0800 Subject: bcache: New writeback PD controller The old writeback PD controller could get into states where it had throttled all the way down and take way too long to recover - it was too complicated to really understand what it was doing. This rewrites a good chunk of it to hopefully be simpler and make more sense, and it also pays more attention to units which should make the behaviour a bit easier to understand. Signed-off-by: Kent Overstreet --- drivers/md/bcache/writeback.c | 47 +++++++++++++++++++++---------------------- 1 file changed, 23 insertions(+), 24 deletions(-) (limited to 'drivers/md/bcache/writeback.c') diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c index 3cd931d3f26c..6c44fe059c27 100644 --- a/drivers/md/bcache/writeback.c +++ b/drivers/md/bcache/writeback.c @@ -30,38 +30,40 @@ static void __update_writeback_rate(struct cached_dev *dc) /* PD controller */ - int change = 0; - int64_t error; int64_t dirty = bcache_dev_sectors_dirty(&dc->disk); int64_t derivative = dirty - dc->disk.sectors_dirty_last; + int64_t proportional = dirty - target; + int64_t change; dc->disk.sectors_dirty_last = dirty; - derivative *= dc->writeback_rate_d_term; - derivative = clamp(derivative, -dirty, dirty); + /* Scale to sectors per second */ - derivative = ewma_add(dc->disk.sectors_dirty_derivative, derivative, - dc->writeback_rate_d_smooth, 0); + proportional *= dc->writeback_rate_update_seconds; + proportional = div_s64(proportional, dc->writeback_rate_p_term_inverse); - /* Avoid divide by zero */ - if (!target) - goto out; + derivative = div_s64(derivative, dc->writeback_rate_update_seconds); - error = div64_s64((dirty + derivative - target) << 8, target); + derivative = ewma_add(dc->disk.sectors_dirty_derivative, derivative, + (dc->writeback_rate_d_term / + dc->writeback_rate_update_seconds) ?: 1, 0); + + derivative *= dc->writeback_rate_d_term; + derivative = div_s64(derivative, dc->writeback_rate_p_term_inverse); - change = div_s64((dc->writeback_rate.rate * error) >> 8, - dc->writeback_rate_p_term_inverse); + change = proportional + derivative; /* Don't increase writeback rate if the device isn't keeping up */ if (change > 0 && time_after64(local_clock(), - dc->writeback_rate.next + 10 * NSEC_PER_MSEC)) + dc->writeback_rate.next + NSEC_PER_MSEC)) change = 0; dc->writeback_rate.rate = - clamp_t(int64_t, dc->writeback_rate.rate + change, + clamp_t(int64_t, (int64_t) dc->writeback_rate.rate + change, 1, NSEC_PER_MSEC); -out: + + dc->writeback_rate_proportional = proportional; dc->writeback_rate_derivative = derivative; dc->writeback_rate_change = change; dc->writeback_rate_target = target; @@ -87,15 +89,11 @@ static void update_writeback_rate(struct work_struct *work) static unsigned writeback_delay(struct cached_dev *dc, unsigned sectors) { - uint64_t ret; - if (test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags) || !dc->writeback_percent) return 0; - ret = bch_next_delay(&dc->writeback_rate, sectors * 10000000ULL); - - return min_t(uint64_t, ret, HZ); + return bch_next_delay(&dc->writeback_rate, sectors); } struct dirty_io { @@ -476,6 +474,8 @@ void bch_sectors_dirty_init(struct cached_dev *dc) bch_btree_map_keys(&op.op, dc->disk.c, &KEY(op.inode, 0, 0), sectors_dirty_init_fn, 0); + + dc->disk.sectors_dirty_last = bcache_dev_sectors_dirty(&dc->disk); } int bch_cached_dev_writeback_init(struct cached_dev *dc) @@ -490,10 +490,9 @@ int bch_cached_dev_writeback_init(struct cached_dev *dc) dc->writeback_delay = 30; dc->writeback_rate.rate = 1024; - dc->writeback_rate_update_seconds = 30; - dc->writeback_rate_d_term = 16; - dc->writeback_rate_p_term_inverse = 64; - dc->writeback_rate_d_smooth = 8; + dc->writeback_rate_update_seconds = 5; + dc->writeback_rate_d_term = 30; + dc->writeback_rate_p_term_inverse = 6000; dc->writeback_thread = kthread_create(bch_writeback_thread, dc, "bcache_writeback"); -- cgit v1.2.3