Re: [PATCH] bcache: fix issue of writeback rate at minimum 1 block per second
From: Coly Li <hidden>
Date: 2017-06-08 16:00:43
On 2017/6/8 下午5:34, tang.junhui@zte.com.cn wrote:
From: Tang Junhui <redacted> When there is not enough data in writeback cache, let the writeback rate to be 0, and delay 30 seconds in read_dirty().
I feel uncomfortable to the above idea. Is the purpose of this change is to make writeback more efficient with more dirty data ? Or some other reason that you want to make this change? When data writing back to the backing device, most of the writes are random. If the backing device is a hard disk, the write back rate will be very slow. Such a longer delay only makes more data accumulated in writeback cache, does not help the writeback rate indeed. Do you observe performance improvement by this patch ? If yes, I'd like to see the performance number. Thanks. Coly
quoted hunk ↗ jump to hunk
Signed-off-by: Tang Junhui <redacted> --- drivers/md/bcache/util.c | 17 ++++++++++++----- drivers/md/bcache/writeback.c | 2 +- 2 files changed, 13 insertions(+), 6 deletions(-)diff --git a/drivers/md/bcache/util.c b/drivers/md/bcache/util.c index dde6172..cf750df 100644 --- a/drivers/md/bcache/util.c +++ b/drivers/md/bcache/util.c@@ -15,6 +15,8 @@ #include "util.h" +#define ZERO_RATE_DELAY_NS 30*NSEC_PER_SEC + #define simple_strtoint(c, end, base) simple_strtol(c, end, base) #define simple_strtouint(c, end, base) simple_strtoul(c, end, base)@@ -209,13 +211,18 @@ uint64_t bch_next_delay(struct bch_ratelimit *d, uint64_t done) { uint64_t now = local_clock(); - d->next += div_u64(done * NSEC_PER_SEC, d->rate); + if (!d->rate) { + d->next = now + ZERO_RATE_DELAY_NS; + } + else { + d->next += div_u64(done * NSEC_PER_SEC, d->rate); - if (time_before64(now + NSEC_PER_SEC, d->next)) - d->next = now + NSEC_PER_SEC; + if (time_before64(now + NSEC_PER_SEC, d->next)) + d->next = now + NSEC_PER_SEC; - if (time_after64(now - NSEC_PER_SEC * 2, d->next)) - d->next = now - NSEC_PER_SEC * 2; + if (time_after64(now - NSEC_PER_SEC * 2, d->next)) + d->next = now - NSEC_PER_SEC * 2; + } return time_after64(d->next, now) ? div_u64(d->next - now, NSEC_PER_SEC / HZ)diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c index 69e1ae5..8fac280 100644 --- a/drivers/md/bcache/writeback.c +++ b/drivers/md/bcache/writeback.c@@ -60,7 +60,7 @@ static void __update_writeback_rate(struct cached_dev *dc) dc->writeback_rate.rate = clamp_t(int64_t, (int64_t) dc->writeback_rate.rate + change, - 1, NSEC_PER_MSEC); + 0, NSEC_PER_MSEC); dc->writeback_rate_proportional = proportional; dc->writeback_rate_derivative = derivative;