When there is only one type of traffic, the associated last_low_overflow_time will not be updated, so the value is stale and invalid and we should discard it. Otherwise, __tg_last_low_overflow_time always return the stale value because it is smaller, and then we always get bps/iops has been below low limit for 1 throtl_slice, and limit_index will jump down and up between LOW and MAX, the actual bps/iops stays on low_limit. Add last_submit_time[2] into tg to track the time when bio enters into blk_throtl_bio. If there is no bio entering during past 5 throtl_slices, and the actual dispatching bps/iops are indeed lower than low limit, return 0 as the last_low_overflow_time which indicates it is stale. We will discard the stale last_low_overflow_time, but if both types are stale, return 0, Otherwise, the cgroups which don't have any traffic will prevent upgrade. Signed-off-by: Jianchao Wang <jianchao.w.wang@xxxxxxxxxx> --- block/blk-throttle.c | 37 ++++++++++++++++++++++++++++++++++--- 1 file changed, 34 insertions(+), 3 deletions(-) diff --git a/block/blk-throttle.c b/block/blk-throttle.c index c5a1316..851aa16 100644 --- a/block/blk-throttle.c +++ b/block/blk-throttle.c @@ -158,6 +158,7 @@ struct throtl_grp { unsigned int io_disp[2]; unsigned long last_low_overflow_time[2]; + unsigned long last_submit_time[2]; uint64_t last_bytes_disp[2]; unsigned int last_io_disp[2]; @@ -1752,15 +1753,42 @@ static struct blkcg_policy blkcg_policy_throtl = { .pd_free_fn = throtl_pd_free, }; +/* + * If there is no any traffic of type 'rw' into blk_throtl_bio during + * past 5 throtl_slice, AND the actual dispatching bps/iops of type 'rw' + * is indeed lower than low limit, we return 0 as the last_low_overflow_time + * which indicates it is stale. + */ +static inline unsigned long tg_return_lloft(struct throtl_grp *tg, + unsigned int rw) +{ + unsigned long time = tg->last_low_overflow_time[rw]; + unsigned long now = jiffies; + + if (!time_after(now, + tg->last_submit_time[rw] + 5 * tg->td->throtl_slice)) + return time; + + if (!time_after(now, time + 5 * tg->td->throtl_slice)) + return time; + + return 0; +} + static unsigned long __tg_last_low_overflow_time(struct throtl_grp *tg) { unsigned long rtime = jiffies, wtime = jiffies; if (tg->bps[READ][LIMIT_LOW] || tg->iops[READ][LIMIT_LOW]) - rtime = tg->last_low_overflow_time[READ]; + rtime = tg_return_lloft(tg, READ); if (tg->bps[WRITE][LIMIT_LOW] || tg->iops[WRITE][LIMIT_LOW]) - wtime = tg->last_low_overflow_time[WRITE]; - return min(rtime, wtime); + wtime = tg_return_lloft(tg, WRITE); + + /* + * A cgroup w/o any traffic could have two stale value, return 0 instead + * of 'now', otherwise, it will prevent upgrade. + */ + return (rtime && wtime) ? min(rtime, wtime) : (rtime + wtime); } /* tg should not be an intermediate node */ @@ -2175,8 +2203,11 @@ bool blk_throtl_bio(struct request_queue *q, struct blkcg_gq *blkg, while (true) { if (tg->last_low_overflow_time[rw] == 0) tg->last_low_overflow_time[rw] = jiffies; + if (unlikely(tg->last_submit_time[rw] == 0)) + tg->last_submit_time[rw] = jiffies; throtl_downgrade_check(tg); throtl_upgrade_check(tg); + tg->last_submit_time[rw] = jiffies; /* throtl is FIFO - if bios are already queued, should queue */ if (sq->nr_queued[rw]) break; -- 2.7.4