2011-03-22 22:35:32

by Justin TerAvest

Subject: [PATCH v2] cfq-iosched: Don't clear queue stats when preempt.

For v2, I added back lines to cfq_preempt_queue() that were removed
during updates for accounting unaccounted_time. Thanks for pointing out
that I'd missed these, Vivek.

Previous commit "cfq-iosched: Don't set active queue in preempt" wrongly
cleared stats for preempting queues when it shouldn't have, because when
we choose a queue to preempt, it still isn't necessarily scheduled next.

Thanks to Vivek Goyal for figuring this out and understanding how the
preemption code works.

Signed-off-by: Justin TerAvest <[email protected]>
---
block/cfq-iosched.c | 39 +++++++++++++++++----------------------
1 files changed, 17 insertions(+), 22 deletions(-)

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 69208d7..fea1b5a 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1620,33 +1620,27 @@ static inline void cfq_del_timer(struct cfq_data *cfqd, struct cfq_queue *cfqq)
cfq_blkiocg_update_idle_time_stats(&cfqq->cfqg->blkg);
}

-static void cfq_clear_queue_stats(struct cfq_data *cfqd,
- struct cfq_queue *cfqq)
-{
- cfq_blkiocg_update_avg_queue_size_stats(&cfqq->cfqg->blkg);
- cfqq->slice_start = 0;
- cfqq->dispatch_start = jiffies;
- cfqq->allocated_slice = 0;
- cfqq->slice_end = 0;
- cfqq->slice_dispatch = 0;
- cfqq->nr_sectors = 0;
-
- cfq_clear_cfqq_wait_request(cfqq);
- cfq_clear_cfqq_must_dispatch(cfqq);
- cfq_clear_cfqq_must_alloc_slice(cfqq);
- cfq_clear_cfqq_fifo_expire(cfqq);
- cfq_mark_cfqq_slice_new(cfqq);
-
- cfq_del_timer(cfqd, cfqq);
-}
-
static void __cfq_set_active_queue(struct cfq_data *cfqd,
struct cfq_queue *cfqq)
{
if (cfqq) {
cfq_log_cfqq(cfqd, cfqq, "set_active wl_prio:%d wl_type:%d",
cfqd->serving_prio, cfqd->serving_type);
- cfq_clear_queue_stats(cfqd, cfqq);
+ cfq_blkiocg_update_avg_queue_size_stats(&cfqq->cfqg->blkg);
+ cfqq->slice_start = 0;
+ cfqq->dispatch_start = jiffies;
+ cfqq->allocated_slice = 0;
+ cfqq->slice_end = 0;
+ cfqq->slice_dispatch = 0;
+ cfqq->nr_sectors = 0;
+
+ cfq_clear_cfqq_wait_request(cfqq);
+ cfq_clear_cfqq_must_dispatch(cfqq);
+ cfq_clear_cfqq_must_alloc_slice(cfqq);
+ cfq_clear_cfqq_fifo_expire(cfqq);
+ cfq_mark_cfqq_slice_new(cfqq);
+
+ cfq_del_timer(cfqd, cfqq);
}

cfqd->active_queue = cfqq;
@@ -3339,7 +3333,8 @@ static void cfq_preempt_queue(struct cfq_data *cfqd, struct cfq_queue *cfqq)

cfq_service_tree_add(cfqd, cfqq, 1);

- cfq_clear_queue_stats(cfqd, cfqq);
+ cfqq->slice_end = 0;
+ cfq_mark_cfqq_slice_new(cfqq);
}

/*
--
1.7.3.1

2011-03-23 07:31:35

by Jens Axboe

Subject: Re: [PATCH v2] cfq-iosched: Don't clear queue stats when preempt.

On 2011-03-22 23:35, Justin TerAvest wrote:
> For v2, I added back lines to cfq_preempt_queue() that were removed
> during updates for accounting unaccounted_time. Thanks for pointing out
> that I'd missed these, Vivek.
>
> Previous commit "cfq-iosched: Don't set active queue in preempt" wrongly
> cleared stats for preempting queues when it shouldn't have, because when
> we choose a queue to preempt, it still isn't necessarily scheduled next.
>
> Thanks to Vivek Goyal for figuring this out and understanding how the
> preemption code works.

Thanks to both of you, applied.

--
Jens Axboe