在 2022/9/19 12:38, Coly Li 写道:
2022年9月19日 11:29，mingzhe <mingzhe.zou@xxxxxxxxxxxx> 写道： 在 2022/9/18 20:16, Coly Li 写道:Inside set_at_max_writeback_rate() the calculation in following if() check is wrong, if (atomic_inc_return(&c->idle_counter) < atomic_read(&c->attached_dev_nr) * 6) Because each attached backing device has its own writeback thread running and increasing c->idle_counter, the counter increates much faster than expected. The correct calculation should be, (counter / dev_nr) < dev_nr * 6 which equals to, counter < dev_nr * dev_nr * 6 This patch fixes the above mistake with correct calculation, and helper routine idle_counter_exceeded() is added to make code be more clear. Reported-by: Mingzhe Zou <mingzhe.zou@xxxxxxxxxxxx> Signed-off-by: Coly Li <colyli@xxxxxxx> --- Changelog: v2: Add the missing "!atomic_read(&c->at_max_writeback_rate)" part back. v1: Original verison. drivers/md/bcache/writeback.c | 73 +++++++++++++++++++++++++---------- 1 file changed, 52 insertions(+), 21 deletions(-) diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c index 647661005176..c186bf55fe61 100644 --- a/drivers/md/bcache/writeback.c +++ b/drivers/md/bcache/writeback.c @@ -157,6 +157,53 @@ static void __update_writeback_rate(struct cached_dev *dc) dc->writeback_rate_target = target; } +static bool idle_counter_exceeded(struct cache_set *c) +{ + int counter, dev_nr; + + /* + * If c->idle_counter is overflow (idel for really long time), + * reset as 0 and not set maximum rate this time for code + * simplicity. + */ + counter = atomic_inc_return(&c->idle_counter); + if (counter <= 0) { + atomic_set(&c->idle_counter, 0); + return false; + } + + dev_nr = atomic_read(&c->attached_dev_nr); + if (dev_nr == 0) + return false; + + /* + * c->idle_counter is increased by writeback thread of all + * attached backing devices, in order to represent a rough + * time period, counter should be divided by dev_nr. + * Otherwise the idle time cannot be larger with more backing + * device attached. + * The following calculation equals to checking + * (counter / dev_nr) < (dev_nr * 6) + */ + if (counter < (dev_nr * dev_nr * 6)) + return false;Hi, Coly
BTW, if the patch looks fine to you, could you please to response a Reviewed-by or Acked-by for it? Thanks. Coly Li
Acked-by: Mingzhe Zou <mingzhe.zou@xxxxxxxxxxxx> Thanks mingzhe
