Re: [PATCH RFC v7 02/12] blk-mq: rename blk_mq_update_tag_set_depth()

Hannes Reinecke
2020-06-23T14:23:37Z

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On 6/23/20 1:25 PM, John Garry wrote:
> On 11/06/2020 09:26, John Garry wrote:
>> On 11/06/2020 03:57, Ming Lei wrote:
>>> On Thu, Jun 11, 2020 at 01:29:09AM +0800, John Garry wrote:
>>>> From: Hannes Reinecke <hare@suse.de>
>>>>
>>>> The function does not set the depth, but rather transitions from
>>>> shared to non-shared queues and vice versa.
>>>> So rename it to blk_mq_update_tag_set_shared() to better reflect
>>>> its purpose.
>>>
>>> It is fine to rename it for me, however:
>>>
>>> This patch claims to rename blk_mq_update_tag_set_shared(), but also
>>> change blk_mq_init_bitmap_tags's signature.
>>
>> I was going to update the commit message here, but forgot again...
>>
>>>
>>> So suggest to split this patch into two or add comment log on changing
>>> blk_mq_init_bitmap_tags().
>>
>> I think I'll just split into 2x commits.
>
> Hi Hannes,
>
> Do you have any issue with splitting the undocumented changes into
> another patch as so:
>
No, that's perfectly fine.

Kashyap, I've also attached an updated patch for the elevator_count
patch; if you agree John can include it in the next version.

Cheers,

Hannes
--
Dr. Hannes Reinecke Teamlead Storage & Networking
hare@suse.de +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer

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From d50b5f773713070208c405f7c7056eb1afed896a Mon Sep 17 00:00:00 2001
From: Hannes Reinecke <hare@suse.de>
Date: Tue, 23 Jun 2020 16:18:40 +0200
Subject: [PATCH] elevator: count requests per hctx to improve performance

Add a 'elevator_queued' count to the hctx to avoid triggering
the elevator even though there are no requests queued.

Suggested-by: Kashyap Desai <kashyap.desai@broadcom.com>
Signed-off-by: Hannes Reinecke <hare@suse.de>
---
block/bfq-iosched.c | 5 +++++
block/blk-mq.c | 1 +
block/mq-deadline.c | 5 +++++
include/linux/blk-mq.h | 4 ++++
4 files changed, 15 insertions(+)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index a1123d4d586d..3d63b35f6121 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -4640,6 +4640,9 @@ static bool bfq_has_work(struct blk_mq_hw_ctx *hctx)
{
struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;

+ if (!atomic_read(&hctx->elevator_queued))
+ return false;
+
/*
* Avoiding lock: a race on bfqd->busy_queues should cause at
* most a call to dispatch for nothing
@@ -5554,6 +5557,7 @@ static void bfq_insert_requests(struct blk_mq_hw_ctx *hctx,
rq = list_first_entry(list, struct request, queuelist);
list_del_init(&rq->queuelist);
bfq_insert_request(hctx, rq, at_head);
+ atomic_inc(&hctx->elevator_queued)
}
}

@@ -5933,6 +5937,7 @@ static void bfq_finish_requeue_request(struct request *rq)

bfq_completed_request(bfqq, bfqd);
bfq_finish_requeue_request_body(bfqq);
+ atomic_dec(&rq->mq_hctx->elevator_queued);

spin_unlock_irqrestore(&bfqd->lock, flags);
} else {
diff --git a/block/blk-mq.c b/block/blk-mq.c
index e06e8c9f326f..f5403fc97572 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2542,6 +2542,7 @@ blk_mq_alloc_hctx(struct request_queue *q, struct blk_mq_tag_set *set,
goto free_hctx;

atomic_set(&hctx->nr_active, 0);
+ atomic_set(&hctx->elevator_queued, 0);
if (node == NUMA_NO_NODE)
node = set->numa_node;
hctx->numa_node = node;
diff --git a/block/mq-deadline.c b/block/mq-deadline.c
index b57470e154c8..9d753745e6be 100644
--- a/block/mq-deadline.c
+++ b/block/mq-deadline.c
@@ -533,6 +533,7 @@ static void dd_insert_requests(struct blk_mq_hw_ctx *hctx,
rq = list_first_entry(list, struct request, queuelist);
list_del_init(&rq->queuelist);
dd_insert_request(hctx, rq, at_head);
+ atomic_inc(&hctx->elevator_queued);
}
spin_unlock(&dd->lock);
}
@@ -573,12 +574,16 @@ static void dd_finish_request(struct request *rq)
blk_mq_sched_mark_restart_hctx(rq->mq_hctx);
spin_unlock_irqrestore(&dd->zone_lock, flags);
}
+ atomic_dec(&rq->mq_hctx->elevator_queued);
}

static bool dd_has_work(struct blk_mq_hw_ctx *hctx)
{
struct deadline_data *dd = hctx->queue->elevator->elevator_data;

+ if (!atomic_read(&hctx->elevator_queued))
+ return false;
+
return !list_empty_careful(&dd->dispatch) ||
!list_empty_careful(&dd->fifo_list[0]) ||
!list_empty_careful(&dd->fifo_list[1]);
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 66711c7234db..a18c506b14e7 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -139,6 +139,10 @@ struct blk_mq_hw_ctx {
* shared across request queues.
*/
atomic_t nr_active;
+ /**
+ * @elevator_queued: Number of queued requests on hctx.
+ */
+ atomic_t elevator_queued;

/** @cpuhp_online: List to store request if CPU is going to die */
struct hlist_node cpuhp_online;
--
2.26.2