From a8394090a9129b40f9d90dcb7f4a49d60c727ca6 Mon Sep 17 00:00:00 2001 From: Tang Junhui Date: Wed, 6 Sep 2017 14:25:56 +0800 Subject: [PATCH] bcache: correct cache_dirty_target in __update_writeback_rate() __update_write_rate() uses a Proportion-Differentiation Controller algorithm to control writeback rate. A dirty target number is used in this PD controller to control writeback rate. A larger target number will make the writeback rate smaller, on the versus, a smaller target number will make the writeback rate larger. bcache uses the following steps to calculate the target number, 1) cache_sectors = all-buckets-of-cache-set * buckets-size 2) cache_dirty_target = cache_sectors * cached-device-writeback_percent 3) target = cache_dirty_target * (sectors-of-cached-device/sectors-of-all-cached-devices-of-this-cache-set) The calculation at step 1) for cache_sectors is incorrect, which does not consider dirty blocks occupied by flash only volume. A flash only volume can be took as a bcache device without cached device. All data sectors allocated for it are persistent on cache device and marked dirty, they are not touched by bcache writeback and garbage collection code. So data blocks of flash only volume should be ignore when calculating cache_sectors of cache set. Current code does not subtract dirty sectors of flash only volume, which results a larger target number from the above 3 steps. And in sequence the cache device's writeback rate is smaller then a correct value, writeback speed is slower on all cached devices. This patch fixes the incorrect slower writeback rate by subtracting dirty sectors of flash only volumes in __update_writeback_rate(). (Commit log composed by Coly Li to pass checkpatch.pl checking) Signed-off-by: Tang Junhui Reviewed-by: Coly Li Cc: stable@vger.kernel.org Signed-off-by: Jens Axboe --- drivers/md/bcache/writeback.c | 3 ++- drivers/md/bcache/writeback.h | 19 +++++++++++++++++++ 2 files changed, 21 insertions(+), 1 deletion(-) diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c index c49022a8dc9d..5abe6472b66b 100644 --- a/drivers/md/bcache/writeback.c +++ b/drivers/md/bcache/writeback.c @@ -21,7 +21,8 @@ static void __update_writeback_rate(struct cached_dev *dc) { struct cache_set *c = dc->disk.c; - uint64_t cache_sectors = c->nbuckets * c->sb.bucket_size; + uint64_t cache_sectors = c->nbuckets * c->sb.bucket_size - + bcache_flash_devs_sectors_dirty(c); uint64_t cache_dirty_target = div_u64(cache_sectors * dc->writeback_percent, 100); diff --git a/drivers/md/bcache/writeback.h b/drivers/md/bcache/writeback.h index 629bd1a502fd..8789b9c8c484 100644 --- a/drivers/md/bcache/writeback.h +++ b/drivers/md/bcache/writeback.h @@ -14,6 +14,25 @@ static inline uint64_t bcache_dev_sectors_dirty(struct bcache_device *d) return ret; } +static inline uint64_t bcache_flash_devs_sectors_dirty(struct cache_set *c) +{ + uint64_t i, ret = 0; + + mutex_lock(&bch_register_lock); + + for (i = 0; i < c->nr_uuids; i++) { + struct bcache_device *d = c->devices[i]; + + if (!d || !UUID_FLASH_ONLY(&c->uuids[i])) + continue; + ret += bcache_dev_sectors_dirty(d); + } + + mutex_unlock(&bch_register_lock); + + return ret; +} + static inline unsigned offset_to_stripe(struct bcache_device *d, uint64_t offset) { -- 2.20.1