On Mon, Sep 25, 2017 at 06:46:42PM +0800, Joseph Qi wrote: > From: Joseph Qi <[email protected]> > > Currently it will try to dispatch bio in throtl_upgrade_state. This may > lead to io stall in the following case. > Say the hierarchy is like: > /-test1 > |-subtest1 > and subtest1 has 32 queued bios now. > > throtl_pending_timer_fn throtl_upgrade_state > ------------------------------------------------------------------------ > upgrade to max > throtl_select_dispatch > throtl_schedule_next_dispatch > throtl_select_dispatch > throtl_schedule_next_dispatch > > Since throtl_select_dispatch will move queued bios from subtest1 to > test1 in throtl_upgrade_state, it will then just do nothing in > throtl_pending_timer_fn. As a result, queued bios won't be dispatched > any more if no proper timer scheduled.
Sorry, didn't get it. If throtl_pending_timer_fn does nothing (because throtl_upgrade_state already moves bios to parent), there is no pending blkcg/bio, not rearming the timer wouldn't lose anything. Am I missing anything? could you please describe the failure in details? Thanks, Shaohua > Fix this issue by just scheduling dispatch now and let the dispatch be > done only in timer. > > Signed-off-by: Joseph Qi <[email protected]> > --- > block/blk-throttle.c | 8 +++----- > 1 file changed, 3 insertions(+), 5 deletions(-) > > diff --git a/block/blk-throttle.c b/block/blk-throttle.c > index 0fea76a..29d282f 100644 > --- a/block/blk-throttle.c > +++ b/block/blk-throttle.c > @@ -1909,13 +1909,11 @@ static void throtl_upgrade_state(struct throtl_data > *td) > struct throtl_grp *tg = blkg_to_tg(blkg); > struct throtl_service_queue *sq = &tg->service_queue; > > - tg->disptime = jiffies - 1; > - throtl_select_dispatch(sq); > - throtl_schedule_next_dispatch(sq, false); > + tg->disptime = jiffies; > + throtl_schedule_next_dispatch(sq, true); > } > rcu_read_unlock(); > - throtl_select_dispatch(&td->service_queue); > - throtl_schedule_next_dispatch(&td->service_queue, false); > + throtl_schedule_next_dispatch(&td->service_queue, true); > queue_work(kthrotld_workqueue, &td->dispatch_work); > } > > -- > 1.9.4
