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authorYu Kuai <yukuai3@huawei.com>2024-04-11 06:23:48 +0300
committerJens Axboe <axboe@kernel.dk>2024-04-12 17:31:54 +0300
commit3ec4848913d695245716ea45ca4872d9dff097a5 (patch)
tree605813986d8a205fbd59488c1b68e68b4b864861
parent013ee5a6234d4c574dedd60c4887a4bcc9ecc749 (diff)
downloadlinux-3ec4848913d695245716ea45ca4872d9dff097a5.tar.xz
block: fix that blk_time_get_ns() doesn't update time after schedule
While monitoring the throttle time of IO from iocost, it's found that such time is always zero after the io_schedule() from ioc_rqos_throttle, for example, with the following debug patch: + printk("%s-%d: %s enter %llu\n", current->comm, current->pid, __func__, blk_time_get_ns()); while (true) { set_current_state(TASK_UNINTERRUPTIBLE); if (wait.committed) break; io_schedule(); } + printk("%s-%d: %s exit %llu\n", current->comm, current->pid, __func__, blk_time_get_ns()); It can be observerd that blk_time_get_ns() always return the same time: [ 1068.096579] fio-1268: ioc_rqos_throttle enter 1067901962288 [ 1068.272587] fio-1268: ioc_rqos_throttle exit 1067901962288 [ 1068.274389] fio-1268: ioc_rqos_throttle enter 1067901962288 [ 1068.472690] fio-1268: ioc_rqos_throttle exit 1067901962288 [ 1068.474485] fio-1268: ioc_rqos_throttle enter 1067901962288 [ 1068.672656] fio-1268: ioc_rqos_throttle exit 1067901962288 [ 1068.674451] fio-1268: ioc_rqos_throttle enter 1067901962288 [ 1068.872655] fio-1268: ioc_rqos_throttle exit 1067901962288 And I think the root cause is that 'PF_BLOCK_TS' is always cleared by blk_flush_plug() before scheduel(), hence blk_plug_invalidate_ts() will never be called: blk_time_get_ns plug->cur_ktime = ktime_get_ns(); current->flags |= PF_BLOCK_TS; io_schedule: io_schedule_prepare blk_flush_plug __blk_flush_plug /* the flag is cleared, while time is not */ current->flags &= ~PF_BLOCK_TS; schedule sched_update_worker /* the flag is not set, hence plug->cur_ktime is not cleared */ if (tsk->flags & PF_BLOCK_TS) blk_plug_invalidate_ts() blk_time_get_ns /* got the time stashed before schedule */ return plug->cur_ktime; Fix the problem by clearing cached time in __blk_flush_plug(). Fixes: 06b23f92af87 ("block: update cached timestamp post schedule/preemption") Signed-off-by: Yu Kuai <yukuai3@huawei.com> Link: https://lore.kernel.org/r/20240411032349.3051233-2-yukuai1@huaweicloud.com Signed-off-by: Jens Axboe <axboe@kernel.dk>
-rw-r--r--block/blk-core.c1
1 files changed, 1 insertions, 0 deletions
diff --git a/block/blk-core.c b/block/blk-core.c
index 3a6f5603fb44..b795ac177281 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1197,6 +1197,7 @@ void __blk_flush_plug(struct blk_plug *plug, bool from_schedule)
if (unlikely(!rq_list_empty(plug->cached_rq)))
blk_mq_free_plug_rqs(plug);
+ plug->cur_ktime = 0;
current->flags &= ~PF_BLOCK_TS;
}