From: John Garry <john.garry@huawei.com>
To: Hannes Reinecke <hare@suse.de>, <axboe@kernel.dk>,
<jejb@linux.ibm.com>, <martin.petersen@oracle.com>,
<don.brace@microsemi.com>, <kashyap.desai@broadcom.com>,
<sumit.saxena@broadcom.com>, <ming.lei@redhat.com>,
<bvanassche@acm.org>, <hare@suse.com>, <hch@lst.de>,
<shivasharan.srikanteshwara@broadcom.com>
Cc: <linux-block@vger.kernel.org>, <linux-scsi@vger.kernel.org>,
<esc.storagedev@microsemi.com>, <chenxiang66@hisilicon.com>,
<megaraidlinux.pdl@broadcom.com>
Subject: Re: [PATCH RFC v7 06/12] blk-mq: Record active_queues_shared_sbitmap per tag_set for when using shared sbitmap
Date: Thu, 11 Jun 2020 15:22:50 +0100 [thread overview]
Message-ID: <8bafb633-de7c-8b9e-7369-8e59c93712f8@huawei.com> (raw)
In-Reply-To: <a10a20de-d8e2-8505-65ec-1c26bfbf6cfc@suse.de>
>> out:
>> @@ -802,6 +822,7 @@ static const struct blk_mq_debugfs_attr
>> blk_mq_debugfs_hctx_shared_sbitmap_attrs
>> {"dispatch", 0400, .seq_ops = &hctx_dispatch_seq_ops},
>> {"busy", 0400, hctx_busy_show},
>> {"ctx_map", 0400, hctx_ctx_map_show},
>> + {"tags", 0400, hctx_tags_show},
>> {"sched_tags", 0400, hctx_sched_tags_show},
>> {"sched_tags_bitmap", 0400, hctx_sched_tags_bitmap_show},
>> {"io_poll", 0600, hctx_io_poll_show, hctx_io_poll_write},
>
> I had been pondering this, too, when creating v6. Problem is that it'll
> show the tags per hctx, but as they are shared I guess the list looks
> pretty identical per hctx.
Right, so my main concern in this series is debugfs, and how to present
the tag/hctx info. We can hide things under the hood mostly, but not so
much for debugfs.
> So I guess we should filter the tags per hctx to have only those active
> on that hctx displayed. But when doing so we can only print the
> in-flight tags, the others are not assigned to a hctx and as such we
> can't make a decision on which hctx they'll end up.
So we filter the tags in 7/12, and that should be ok.
But a concern is that we present identical hctx_tags_show() ->
blk_mq_debugfs_shared_sitmap_show() -> sbitmap_queue_show() per-hctx
info, which may be inappropriate/misleading/wrong. I need to audit that
more thoroughly.
>
>> diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
>> index 7db16e49f6f6..6ca06b1c3a99 100644
>> --- a/block/blk-mq-tag.c
>> +++ b/block/blk-mq-tag.c
>> @@ -23,9 +23,19 @@
>> */
>> bool __blk_mq_tag_busy(struct blk_mq_hw_ctx *hctx)
>> {
>> - if (!test_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state) &&
>> - !test_and_set_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
>> - atomic_inc(&hctx->tags->active_queues);
>> + struct request_queue *q = hctx->queue;
>> + struct blk_mq_tag_set *set = q->tag_set;
>> +
>> + if (blk_mq_is_sbitmap_shared(set)){
>> + if (!test_bit(QUEUE_FLAG_HCTX_ACTIVE, &q->queue_flags) &&
>> + !test_and_set_bit(QUEUE_FLAG_HCTX_ACTIVE, &q->queue_flags))
>> + atomic_inc(&set->active_queues_shared_sbitmap);
>> +
>> + } else {
>> + if (!test_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state) &&
>> + !test_and_set_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
>> + atomic_inc(&hctx->tags->active_queues);
>> + }
>> return true;
>> }
> At one point someone would need to educate me what this double
> 'test_bit' and 'test_and_set_bit' is supposed to achieve.
> Other than deliberately injecting a race condition ...
As I see, it's not a dangerous race, and meant as a performance
optimization.
test_bit() should be is quick compared to test_and_set_bit(), so nicer
to avoid always doing a test_and_set_bit().
So if we race with failed test_bit() calls and have multiple attempts
with the test_and_set_bit(), only 1 will succeed and do the increment.
>
>> @@ -47,11 +57,19 @@ void blk_mq_tag_wakeup_all(struct blk_mq_tags
>> *tags, bool include_reserve)
>> void __blk_mq_tag_idle(struct blk_mq_hw_ctx *hctx)
>> {
>> struct blk_mq_tags *tags = hctx->tags;
>> -
>> - if (!test_and_clear_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
>> - return;
>> -
>> - atomic_dec(&tags->active_queues);
>> + struct request_queue *q = hctx->queue;
>> + struct blk_mq_tag_set *set = q->tag_set;
>> +
>> + if (blk_mq_is_sbitmap_shared(q->tag_set)){
>> + if (!test_and_clear_bit(QUEUE_FLAG_HCTX_ACTIVE,
>> + &q->queue_flags))
>> + return;
>> + atomic_dec(&set->active_queues_shared_sbitmap);
>> + } else {
>> + if (!test_and_clear_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
>> + return;
>> + atomic_dec(&tags->active_queues);
>> + }
>> blk_mq_tag_wakeup_all(tags, false);
>> }
>> @@ -65,12 +83,11 @@ static inline bool hctx_may_queue(struct
>> blk_mq_alloc_data *data,
>> {
>> struct blk_mq_hw_ctx *hctx = data->hctx;
>> struct request_queue *q = data->q;
>> + struct blk_mq_tag_set *set = q->tag_set;
>> unsigned int depth, users;
>> if (!hctx || !(hctx->flags & BLK_MQ_F_TAG_QUEUE_SHARED))
>> return true;
>> - if (!test_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
>> - return true;
>> /*
>> * Don't try dividing an ant
>> @@ -78,7 +95,15 @@ static inline bool hctx_may_queue(struct
>> blk_mq_alloc_data *data,
>> if (bt->sb.depth == 1)
>> return true;
>> - users = atomic_read(&hctx->tags->active_queues);
>> + if (blk_mq_is_sbitmap_shared(q->tag_set)) {
>> + if (!test_bit(BLK_MQ_S_TAG_ACTIVE, &q->queue_flags))
>> + return true;
>> + users = atomic_read(&set->active_queues_shared_sbitmap);
>> + } else {
>> + if (!test_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
>> + return true;
>> + users = atomic_read(&hctx->tags->active_queues);
>> + }
>> if (!users)
>> return true;
>> diff --git a/block/blk-mq.c b/block/blk-mq.c
>> index 0f7e062a1665..f73a2f9c58bd 100644
>> --- a/block/blk-mq.c
>> +++ b/block/blk-mq.c
>> @@ -3350,6 +3350,8 @@ int blk_mq_alloc_tag_set(struct blk_mq_tag_set
>> *set)
>> goto out_free_mq_map;
>> if (blk_mq_is_sbitmap_shared(set)) {
>> + atomic_set(&set->active_queues_shared_sbitmap, 0);
>> +
>> if (!blk_mq_init_shared_sbitmap(set)) {
>> ret = -ENOMEM;
>> goto out_free_mq_rq_maps;
>> diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
>> index 7b31cdb92a71..66711c7234db 100644
>> --- a/include/linux/blk-mq.h
>> +++ b/include/linux/blk-mq.h
>> @@ -252,6 +252,7 @@ struct blk_mq_tag_set {
>> unsigned int timeout;
>> unsigned int flags;
>> void *driver_data;
>> + atomic_t active_queues_shared_sbitmap;
I'm not sure if we should present this in debugfs. It is not according
to this series.
>> struct sbitmap_queue __bitmap_tags;
>> struct sbitmap_queue __breserved_tags;
>> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
>> index c536278bec9e..1b0087e8d01a 100644
>> --- a/include/linux/blkdev.h
>> +++ b/include/linux/blkdev.h
>> @@ -619,6 +619,7 @@ struct request_queue {
>> #define QUEUE_FLAG_PCI_P2PDMA 25 /* device supports PCI p2p
>> requests */
>> #define QUEUE_FLAG_ZONE_RESETALL 26 /* supports Zone Reset All */
>> #define QUEUE_FLAG_RQ_ALLOC_TIME 27 /* record rq->alloc_time_ns */
>> +#define QUEUE_FLAG_HCTX_ACTIVE 28 /* at least one blk-mq hctx is
>> active */
>> #define QUEUE_FLAG_MQ_DEFAULT ((1 << QUEUE_FLAG_IO_STAT) | \
>> (1 << QUEUE_FLAG_SAME_COMP))
>>
> Other than that it looks fine.
Cheers
next prev parent reply other threads:[~2020-06-11 14:24 UTC|newest]
Thread overview: 123+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-10 17:29 [PATCH RFC v7 00/12] blk-mq/scsi: Provide hostwide shared tags for SCSI HBAs John Garry
2020-06-10 17:29 ` [PATCH RFC v7 01/12] blk-mq: rename BLK_MQ_F_TAG_SHARED as BLK_MQ_F_TAG_QUEUE_SHARED John Garry
2020-06-10 17:29 ` [PATCH RFC v7 02/12] blk-mq: rename blk_mq_update_tag_set_depth() John Garry
2020-06-11 2:57 ` Ming Lei
2020-06-11 8:26 ` John Garry
2020-06-23 11:25 ` John Garry
2020-06-23 14:23 ` Hannes Reinecke
2020-06-24 8:13 ` Kashyap Desai
2020-06-29 16:18 ` John Garry
2020-08-10 16:51 ` Kashyap Desai
2020-08-11 8:01 ` John Garry
2020-08-11 16:34 ` Kashyap Desai
2020-06-10 17:29 ` [PATCH RFC v7 03/12] blk-mq: Use pointers for blk_mq_tags bitmap tags John Garry
2020-06-10 17:29 ` [PATCH RFC v7 04/12] blk-mq: Facilitate a shared sbitmap per tagset John Garry
2020-06-11 3:37 ` Ming Lei
2020-06-11 10:09 ` John Garry
2020-06-10 17:29 ` [PATCH RFC v7 05/12] blk-mq: Record nr_active_requests per queue for when using shared sbitmap John Garry
2020-06-11 4:04 ` Ming Lei
2020-06-11 10:22 ` John Garry
2020-06-10 17:29 ` [PATCH RFC v7 06/12] blk-mq: Record active_queues_shared_sbitmap per tag_set " John Garry
2020-06-11 13:16 ` Hannes Reinecke
2020-06-11 14:22 ` John Garry [this message]
2020-06-10 17:29 ` [PATCH RFC v7 07/12] blk-mq: Add support in hctx_tags_bitmap_show() for a " John Garry
2020-06-11 13:19 ` Hannes Reinecke
2020-06-11 14:33 ` John Garry
2020-06-12 6:06 ` Hannes Reinecke
2020-06-29 15:32 ` About sbitmap_bitmap_show() and cleared bits (was Re: [PATCH RFC v7 07/12] blk-mq: Add support in hctx_tags_bitmap_show() for a shared sbitmap) John Garry
2020-06-30 6:33 ` Hannes Reinecke
2020-06-30 7:30 ` John Garry
2020-06-30 11:36 ` John Garry
2020-06-30 14:55 ` Bart Van Assche
2020-07-13 9:41 ` [PATCH RFC v7 07/12] blk-mq: Add support in hctx_tags_bitmap_show() for a shared sbitmap John Garry
2020-07-13 12:20 ` Hannes Reinecke
2020-06-10 17:29 ` [PATCH RFC v7 08/12] scsi: Add template flag 'host_tagset' John Garry
2020-06-10 17:29 ` [PATCH RFC v7 09/12] scsi: hisi_sas: Switch v3 hw to MQ John Garry
2020-06-10 17:29 ` [PATCH RFC v7 10/12] megaraid_sas: switch fusion adapters " John Garry
2020-07-02 10:23 ` Kashyap Desai
2020-07-06 8:23 ` John Garry
2020-07-06 8:45 ` Hannes Reinecke
2020-07-06 9:26 ` John Garry
2020-07-06 9:40 ` Hannes Reinecke
2020-07-06 19:19 ` Kashyap Desai
2020-07-07 7:58 ` John Garry
2020-07-07 14:45 ` Kashyap Desai
2020-07-07 16:17 ` John Garry
2020-07-09 19:01 ` Kashyap Desai
2020-07-10 8:10 ` John Garry
2020-07-13 7:55 ` Kashyap Desai
2020-07-13 8:42 ` John Garry
2020-07-19 19:07 ` Kashyap Desai
2020-07-20 7:23 ` Kashyap Desai
2020-07-20 9:18 ` John Garry
2020-07-21 1:13 ` Ming Lei
2020-07-21 6:53 ` Kashyap Desai
2020-07-22 4:12 ` Ming Lei
2020-07-22 5:30 ` Kashyap Desai
2020-07-22 8:04 ` Ming Lei
2020-07-22 9:32 ` John Garry
2020-07-23 14:07 ` Ming Lei
2020-07-23 17:29 ` John Garry
2020-07-24 2:47 ` Ming Lei
2020-07-28 7:54 ` John Garry
2020-07-28 8:45 ` Ming Lei
2020-07-29 5:25 ` Kashyap Desai
2020-07-29 15:36 ` Ming Lei
2020-07-29 18:31 ` Kashyap Desai
2020-08-04 8:36 ` Ming Lei
2020-08-04 9:27 ` Kashyap Desai
2020-08-05 8:40 ` Ming Lei
2020-08-06 10:25 ` Kashyap Desai
2020-08-06 13:38 ` Ming Lei
2020-08-06 14:37 ` Kashyap Desai
2020-08-06 15:29 ` Ming Lei
2020-08-08 19:05 ` Kashyap Desai
2020-08-09 2:16 ` Ming Lei
2020-08-10 16:38 ` Kashyap Desai
2020-08-11 8:09 ` John Garry
2020-08-04 17:00 ` John Garry
2020-08-05 2:56 ` Ming Lei
2020-07-28 8:01 ` Kashyap Desai
2020-07-08 11:31 ` John Garry
2020-06-10 17:29 ` [PATCH RFC v7 11/12] smartpqi: enable host tagset John Garry
2020-07-14 13:16 ` John Garry
2020-07-14 13:31 ` John Garry
2020-07-14 18:16 ` Don.Brace
2020-07-15 7:28 ` John Garry
2020-07-14 14:02 ` Hannes Reinecke
2020-08-18 8:33 ` John Garry
2020-06-10 17:29 ` [PATCH RFC v7 12/12] hpsa: enable host_tagset and switch to MQ John Garry
2020-07-14 7:37 ` John Garry
2020-07-14 7:41 ` Hannes Reinecke
2020-07-14 7:52 ` John Garry
2020-07-14 8:06 ` Ming Lei
2020-07-14 9:53 ` John Garry
2020-07-14 10:14 ` Ming Lei
2020-07-14 10:43 ` Hannes Reinecke
2020-07-14 10:19 ` Hannes Reinecke
2020-07-14 10:35 ` John Garry
2020-07-14 10:44 ` Ming Lei
2020-07-14 10:52 ` John Garry
2020-07-14 12:04 ` Ming Lei
2020-08-03 20:39 ` Don.Brace
2020-08-04 9:27 ` John Garry
2020-08-04 15:18 ` Don.Brace
2020-08-05 11:21 ` John Garry
2020-08-14 21:04 ` Don.Brace
2020-08-17 8:00 ` John Garry
2020-08-17 18:39 ` Don.Brace
2020-08-18 7:14 ` Hannes Reinecke
2020-07-16 16:14 ` Don.Brace
2020-07-16 19:45 ` Don.Brace
2020-07-17 10:11 ` John Garry
2020-06-11 3:07 ` [PATCH RFC v7 00/12] blk-mq/scsi: Provide hostwide shared tags for SCSI HBAs Ming Lei
2020-06-11 9:35 ` John Garry
2020-06-12 18:47 ` Kashyap Desai
2020-06-15 2:13 ` Ming Lei
2020-06-15 6:57 ` Kashyap Desai
2020-06-16 1:00 ` Ming Lei
2020-06-17 11:26 ` Kashyap Desai
2020-06-22 6:24 ` Hannes Reinecke
2020-06-23 0:55 ` Ming Lei
2020-06-23 11:50 ` Kashyap Desai
2020-06-23 12:11 ` Kashyap Desai
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