Messages in this thread Patch in this message | | | Subject | [patch 2/3]cfq-iosched: schedule dispatch for noidle queue | From | Shaohua Li <> | Date | Mon, 08 Nov 2010 10:07:18 +0800 |
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A queue is idle at cfq_dispatch_requests(), but it gets noidle later. Unless other task explictly does unplug or all requests are drained, we will not deliever requests to the disk even cfq_arm_slice_timer doesn't make the queue idle. For example, cfq_should_idle() returns true because of service_tree->count == 1, and then other queues are added. Note, I didn't see obvious performance impacts so far with the patch, but just thought this could be a problem.
Signed-off-by: Shaohua Li <shaohua.li@intel.com>
--- block/cfq-iosched.c | 23 ++++++++++++++++++++++- 1 file changed, 22 insertions(+), 1 deletion(-)
Index: linux/block/cfq-iosched.c =================================================================== --- linux.orig/block/cfq-iosched.c 2010-11-08 08:41:20.000000000 +0800 +++ linux/block/cfq-iosched.c 2010-11-08 08:43:51.000000000 +0800 @@ -3265,6 +3265,10 @@ cfq_should_preempt(struct cfq_data *cfqd if (cfq_class_rt(new_cfqq) && !cfq_class_rt(cfqq)) return true; + /* An idle queue should not be idle now for some reason */ + if (RB_EMPTY_ROOT(&cfqq->sort_list) && !cfq_should_idle(cfqd, cfqq)) + return true; + if (!cfqd->active_cic || !cfq_cfqq_wait_request(cfqq)) return false; @@ -3508,8 +3512,25 @@ static void cfq_completed_request(struct } } - if (!cfqd->rq_in_driver) + if (!cfqd->rq_in_driver) { cfq_schedule_dispatch(cfqd); + return; + } + /* + * A queue is idle at cfq_dispatch_requests(), but it gets noidle + * later. We schedule a dispatch if the queue has no requests, + * otherwise the disk is actually in idle till all requests + * are finished even cfq_arm_slice_timer doesn't make the queue idle + * */ + cfqq = cfqd->active_queue; + if (!cfqq) + return; + + if (RB_EMPTY_ROOT(&cfqq->sort_list) && !cfq_should_idle(cfqd, cfqq) && + (!cfqd->cfq_group_idle || cfqq->cfqg->nr_cfqq > 1)) { + cfq_del_timer(cfqd, cfqq); + cfq_schedule_dispatch(cfqd); + } } /*
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