From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 686AEC433DF for ; Thu, 11 Jun 2020 14:24:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 451312065C for ; Thu, 11 Jun 2020 14:24:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728173AbgFKOYP (ORCPT ); Thu, 11 Jun 2020 10:24:15 -0400 Received: from lhrrgout.huawei.com ([185.176.76.210]:2302 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726414AbgFKOYP (ORCPT ); Thu, 11 Jun 2020 10:24:15 -0400 Received: from lhreml724-chm.china.huawei.com (unknown [172.18.7.108]) by Forcepoint Email with ESMTP id 147FADAAA204334EE69F; Thu, 11 Jun 2020 15:24:11 +0100 (IST) Received: from [127.0.0.1] (10.210.169.30) by lhreml724-chm.china.huawei.com (10.201.108.75) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.1913.5; Thu, 11 Jun 2020 15:24:09 +0100 Subject: Re: [PATCH RFC v7 06/12] blk-mq: Record active_queues_shared_sbitmap per tag_set for when using shared sbitmap To: Hannes Reinecke , , , , , , , , , , , CC: , , , , References: <1591810159-240929-1-git-send-email-john.garry@huawei.com> <1591810159-240929-7-git-send-email-john.garry@huawei.com> From: John Garry Message-ID: <8bafb633-de7c-8b9e-7369-8e59c93712f8@huawei.com> Date: Thu, 11 Jun 2020 15:22:50 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.1.2 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [10.210.169.30] X-ClientProxiedBy: lhreml713-chm.china.huawei.com (10.201.108.64) To lhreml724-chm.china.huawei.com (10.201.108.75) X-CFilter-Loop: Reflected Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org >>   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