Messages in this thread | | | Subject | Re: [PATCH v6 2/2] block: cancel all throttled bios in del_gendisk() | From | "yukuai (C)" <> | Date | Fri, 14 Jan 2022 16:21:04 +0800 |
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在 2022/01/14 11:05, Ming Lei 写道: > On Thu, Jan 13, 2022 at 04:46:18PM +0800, yukuai (C) wrote: >> 在 2022/01/12 11:05, Ming Lei 写道: >>> Hello Yu Kuai, >>> >>> On Mon, Jan 10, 2022 at 09:47:58PM +0800, Yu Kuai wrote: >>>> Throttled bios can't be issued after del_gendisk() is done, thus >>>> it's better to cancel them immediately rather than waiting for >>>> throttle is done. >>>> >>>> For example, if user thread is throttled with low bps while it's >>>> issuing large io, and the device is deleted. The user thread will >>>> wait for a long time for io to return. >>>> >>>> Noted this patch is mainly from revertion of commit 32e3374304c7 >>>> ("blk-throttle: remove tg_drain_bios") and commit b77412372b68 >>>> ("blk-throttle: remove blk_throtl_drain"). >>>> >>>> Signed-off-by: Yu Kuai <yukuai3@huawei.com> >>>> --- >>>> block/blk-throttle.c | 77 ++++++++++++++++++++++++++++++++++++++++++++ >>>> block/blk-throttle.h | 2 ++ >>>> block/genhd.c | 2 ++ >>>> 3 files changed, 81 insertions(+) >>> >>> Just wondering why not take the built-in way in throtl_upgrade_state() for >>> canceling throttled bios? Something like the following, then we can avoid >>> to re-invent the wheel. >>> >>> block/blk-throttle.c | 38 +++++++++++++++++++++++++++++++------- >>> block/blk-throttle.h | 2 ++ >>> block/genhd.c | 3 +++ >>> 3 files changed, 36 insertions(+), 7 deletions(-) >>> >>> diff --git a/block/blk-throttle.c b/block/blk-throttle.c >>> index cf7e20804f1b..17e56b2e44c4 100644 >>> --- a/block/blk-throttle.c >>> +++ b/block/blk-throttle.c >>> @@ -1816,16 +1816,11 @@ static void throtl_upgrade_check(struct throtl_grp *tg) >>> throtl_upgrade_state(tg->td); >>> } >>> -static void throtl_upgrade_state(struct throtl_data *td) >>> +static void __throtl_cancel_bios(struct throtl_data *td) >>> { >>> struct cgroup_subsys_state *pos_css; >>> struct blkcg_gq *blkg; >>> - throtl_log(&td->service_queue, "upgrade to max"); >>> - td->limit_index = LIMIT_MAX; >>> - td->low_upgrade_time = jiffies; >>> - td->scale = 0; >>> - rcu_read_lock(); >>> blkg_for_each_descendant_post(blkg, pos_css, td->queue->root_blkg) { >>> struct throtl_grp *tg = blkg_to_tg(blkg); >>> struct throtl_service_queue *sq = &tg->service_queue; >>> @@ -1834,12 +1829,41 @@ static void throtl_upgrade_state(struct throtl_data *td) >>> throtl_select_dispatch(sq); >>> throtl_schedule_next_dispatch(sq, true); >> Hi, Ming Lei >> >> I'm confused that how can bios be canceled here? >> tg->iops and tg->bps stay untouched, how can throttled bios >> dispatch? > > I thought that throttled bios will be canceled by 'tg->disptime = jiffies - 1;' > and the following dispatch schedule. > > But looks it isn't enough, since tg_update_disptime() updates > ->disptime. However, > this problem can be solved easily by not updating ->disptime in case that we are > canceling. > >>> } >>> - rcu_read_unlock(); >>> throtl_select_dispatch(&td->service_queue); >>> throtl_schedule_next_dispatch(&td->service_queue, true); >>> queue_work(kthrotld_workqueue, &td->dispatch_work); >>> } >>> +void blk_throtl_cancel_bios(struct request_queue *q) >>> +{ >>> + struct cgroup_subsys_state *pos_css; >>> + struct blkcg_gq *blkg; >>> + >>> + rcu_read_lock(); >>> + spin_lock_irq(&q->queue_lock); >>> + __throtl_cancel_bios(q->td); >>> + spin_unlock_irq(&q->queue_lock); >>> + rcu_read_unlock(); >>> + >>> + blkg_for_each_descendant_post(blkg, pos_css, q->root_blkg) >>> + del_timer_sync(&blkg_to_tg(blkg)->service_queue.pending_timer); >>> + del_timer_sync(&q->td->service_queue.pending_timer); >> >> By the way, I think delete timer will end up io hung here if there are >> some bios still be throttled. > > Firstly ->queue_lock is held by blk_throtl_cancel_bios(), so no new bios > will be throttled. > > Also if we don't update ->disptime, any new bios throttled after releasing > ->queue_lock will be dispatched soon.
Hi, Ming Lei
Just to be curiosity, I'm still trying to understand the logic here:
For example, if bps is set to 1k, and a io with size 16k is just dispatched, then io throtle should wait for 16s untill new io can be dispatched. (details in tg_with_in_bps_limit).
How does such mechanism bypassed here?
Thanks, Kuai
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