On Tue, Sep 26, 2017 at 09:06:57AM +0800, Joseph Qi wrote: > Hi Shaohua, > > On 17/9/26 01:22, Shaohua Li wrote: > > On Mon, Sep 25, 2017 at 06:46:42PM +0800, Joseph Qi wrote: > >> From: Joseph Qi <qijiang...@alibaba-inc.com> > >> > >> 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 > >In normal case, throtl_pending_timer_fn tries to move bios from > subtest1 to test1, and finally do the real issueing work when reach > the top-level. > But int the case above, throtl_select_dispatch in > throtl_pending_timer_fn returns 0, because the work is done by > throtl_upgrade_state. Then throtl_pending_timer_fn *thinks* there is > nothing to do, but the queued bios are still in service queue of > test1.
Still didn't get, sorry. If there are pending bios in test1, why throtl_schedule_next_dispatch in throtl_pending_timer_fn doesn't setup the timer?
