On Fri, 23 Jun 2017, tang.junhui@xxxxxxxxxx wrote:
> From: Tang Junhui <tang.junhui@xxxxxxxxxx>
>
> When there is not enough dirty data in writeback cache,
> writeback rate is at minimum 1 key per second
> util all dirty data to be cleaned, it is inefficiency,
> and also causes waste of energy;
>
> in this patch, When there is not enough dirty data,
> let the writeback rate to be 0, and writeback re-schedule
> in bch_writeback_thread() periodically with schedule_timeout(),
> the behaviors are as follows :
>
> 1) If no dirty data have been read into dc->writeback_keys,
> goto step 2), otherwise keep writing these dirty data to
> back-end device at 1 key per second, until all these dirty data
> write over, then goto step 2).
>
> 2) Loop in bch_writeback_thread() to check if there is enough
> dirty data for writeback. if there is not enough diry data for
> writing, then sleep 10 seconds, otherwise, write dirty data to
> back-end device.
>
> Signed-off-by: Tang Junhui <tang.junhui@xxxxxxxxxx>
> ---
> drivers/md/bcache/util.c | 9 ++++++++-
> drivers/md/bcache/writeback.c | 11 +++++++----
> 2 files changed, 15 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/md/bcache/util.c b/drivers/md/bcache/util.c
> index dde6172..d398f09 100644
> --- a/drivers/md/bcache/util.c
> +++ b/drivers/md/bcache/util.c
> @@ -209,7 +209,14 @@ 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 is zero, write the left dirty data
> + at the speed of one key per second
> + */
> + if(!d->rate)
> + d->next = now + NSEC_PER_SEC;
> + 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;
> diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c
> index 69e1ae5..7313643 100644
> --- a/drivers/md/bcache/writeback.c
> +++ b/drivers/md/bcache/writeback.c
> @@ -15,6 +15,8 @@
> #include <linux/kthread.h>
> #include <trace/events/bcache.h>
>
> +#define WRITE_BACK_WAIT_CYCLE 10 * HZ
> +
> /* Rate limiting */
>
> static void __update_writeback_rate(struct cached_dev *dc)
> @@ -54,13 +56,14 @@ static void __update_writeback_rate(struct cached_dev *dc)
>
> /* Don't increase writeback rate if the device isn't keeping up */
> if (change > 0 &&
> + dc->writeback_rate.rate >0 &&
> time_after64(local_clock(),
> dc->writeback_rate.next + NSEC_PER_MSEC))
> change = 0;
>
> 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;
> @@ -419,15 +422,15 @@ static int bch_writeback_thread(void *arg)
> while (!kthread_should_stop()) {
> down_write(&dc->writeback_lock);
> if (!atomic_read(&dc->has_dirty) ||
> - (!test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags) &&
> - !dc->writeback_running)) {
> + ((!dc->writeback_rate.rate || !dc->writeback_running) &&
> + !test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags))) {
> up_write(&dc->writeback_lock);
> set_current_state(TASK_INTERRUPTIBLE);
>
> if (kthread_should_stop())
> return 0;
>
> - schedule();
> + schedule_timeout(WRITE_BACK_WAIT_CYCLE);
Wouldn't bch_writeback_thread need woken up on stop or reboot? Otherwise
it will hang for a while waiting to exit. Correct me if I'm wrong here...
--
Eric Wheeler
> continue;
> }
>
> --
> 2.8.1.windows.1
>
>
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