|author||Vivek Goyal <email@example.com>||2016-09-19 15:12:41 -0600|
|committer||Jens Axboe <firstname.lastname@example.org>||2016-09-19 15:12:41 -0600|
blk-throttle: Extend slice if throttle group is not empty
Right now, if slice is expired, we start a new slice. If a bio is queued, we keep on extending slice by throtle_slice interval (100ms). This worked well as long as pending timer function got executed with-in few milli seconds of scheduled time. But looks like with recent changes in timer subsystem, slack can be much longer depending on the expiry time of the scheduled timer. commit 500462a9de65 ("timers: Switch to a non-cascading wheel") This means, by the time timer function gets executed, it is possible the delay from scheduled time is more than 100ms. That means current code will conclude that existing slice has expired and a new one needs to be started. New slice will be 100ms by default and that will not be sufficient to meet rate requirement of group given the bio size and bio will not be dispatched and we will start a new timer function to wait. And when that timer expires, same process will repeat and we will wait again and this can easily be an infinite loop. Solve this issue by starting a new slice only if throttle gropup is empty. If it is not empty, that means there should be an active slice going on. Ideally it should not be expired but given the slack, it is possible that it has expired. Reported-by: Hou Tao <email@example.com> Signed-off-by: Vivek Goyal <firstname.lastname@example.org> Signed-off-by: Jens Axboe <email@example.com>
Diffstat (limited to 'block/blk-throttle.c')
1 files changed, 4 insertions, 2 deletions
diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index f1aba26..a3ea826 100644
@@ -780,9 +780,11 @@ static bool tg_may_dispatch(struct throtl_grp *tg, struct bio *bio,
* If previous slice expired, start a new one otherwise renew/extend
* existing slice to make sure it is at least throtl_slice interval
- * long since now.
+ * long since now. New slice is started only for empty throttle group.
+ * If there is queued bio, that means there should be an active
+ * slice and it should be extended instead.
- if (throtl_slice_used(tg, rw))
+ if (throtl_slice_used(tg, rw) && !(tg->service_queue.nr_queued[rw]))
if (time_before(tg->slice_end[rw], jiffies + throtl_slice))