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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0095BC433F5 for ; Mon, 18 Oct 2021 09:31:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DB1D660EB1 for ; Mon, 18 Oct 2021 09:31:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231477AbhJRJdj (ORCPT ); Mon, 18 Oct 2021 05:33:39 -0400 Received: from frasgout.his.huawei.com ([185.176.79.56]:3997 "EHLO frasgout.his.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231584AbhJRJdO (ORCPT ); Mon, 18 Oct 2021 05:33:14 -0400 Received: from fraeml709-chm.china.huawei.com (unknown [172.18.147.226]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4HXs2k4gW6z687SH; Mon, 18 Oct 2021 17:26:54 +0800 (CST) Received: from lhreml724-chm.china.huawei.com (10.201.108.75) by fraeml709-chm.china.huawei.com (10.206.15.37) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2308.15; Mon, 18 Oct 2021 11:30:56 +0200 Received: from [10.47.85.98] (10.47.85.98) 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 15.1.2308.15; Mon, 18 Oct 2021 10:30:55 +0100 Subject: Re: [PATCH] blk-mq: Fix blk_mq_tagset_busy_iter() for shared tags To: Ming Lei CC: "axboe@kernel.dk" , "linux-block@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "kashyap.desai@broadcom.com" , "hare@suse.de" References: <1634114459-143003-1-git-send-email-john.garry@huawei.com> <79266509-f327-9de3-d22e-0e9fe00387ee@huawei.com> <9f3c4d57-6b77-5345-0d4c-275962214b2a@huawei.com> <7e142559-1c96-8d84-081a-378c1f6d1306@huawei.com> <1065f517-c94b-5a47-34f6-52015b3ef907@huawei.com> From: John Garry Message-ID: <0e5edb01-08a3-3c97-35e4-97587c864657@huawei.com> Date: Mon, 18 Oct 2021 10:33:47 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.12.1 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: [10.47.85.98] X-ClientProxiedBy: lhreml718-chm.china.huawei.com (10.201.108.69) To lhreml724-chm.china.huawei.com (10.201.108.75) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 18/10/2021 10:07, Ming Lei wrote: > On Mon, Oct 18, 2021 at 09:08:57AM +0100, John Garry wrote: >> On 13/10/2021 16:13, John Garry wrote: >>>> diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c >>>> index 72a2724a4eee..2a2ad6dfcc33 100644 >>>> --- a/block/blk-mq-tag.c >>>> +++ b/block/blk-mq-tag.c >>>> @@ -232,8 +232,9 @@ static bool bt_iter(struct sbitmap *bitmap, >>>> unsigned int bitnr, void *data) >>>>       if (!rq) >>>>           return true; >>>> -    if (rq->q == hctx->queue && rq->mq_hctx == hctx) >>>> -        ret = iter_data->fn(hctx, rq, iter_data->data, reserved); >>>> +    if (rq->q == hctx->queue && (rq->mq_hctx == hctx || >>>> +                blk_mq_is_shared_tags(hctx->flags))) >>>> +        ret = iter_data->fn(rq->mq_hctx, rq, iter_data->data, reserved); >>>>       blk_mq_put_rq_ref(rq); >>>>       return ret; >>>>   } >>>> @@ -460,6 +461,9 @@ void blk_mq_queue_tag_busy_iter(struct >>>> request_queue *q, busy_iter_fn *fn, >>>>           if (tags->nr_reserved_tags) >>>>               bt_for_each(hctx, &tags->breserved_tags, fn, priv, true); >>>>           bt_for_each(hctx, &tags->bitmap_tags, fn, priv, false); >>>> + >>>> +        if (blk_mq_is_shared_tags(hctx->flags)) >>>> +            break; >>>>       } >>>>       blk_queue_exit(q); >>>>   } >>>> >>> I suppose that is ok, and means that we iter once. >>> >>> However, I have to ask, where is the big user of >>> blk_mq_queue_tag_busy_iter() coming from? I saw this from Kashyap's >>> mail: >>> >>> > 1.31%     1.31%  kworker/57:1H-k  [kernel.vmlinux] >>> >       native_queued_spin_lock_slowpath >>> >       ret_from_fork >>> >       kthread >>> >       worker_thread >>> >       process_one_work >>> >       blk_mq_timeout_work >>> >       blk_mq_queue_tag_busy_iter >>> >       bt_iter >>> >       blk_mq_find_and_get_req >>> >       _raw_spin_lock_irqsave >>> >       native_queued_spin_lock_slowpath >>> >>> How or why blk_mq_timeout_work()? >> Just some update: I tried hisi_sas with 10x SAS SSDs, megaraid sas with 1x >> SATA HDD (that's all I have), and null blk with lots of devices, and I still >> can't see high usage of blk_mq_queue_tag_busy_iter(). > It should be triggered easily in case of heavy io accounting: > > while true; do cat /proc/diskstats; done > Let me check that. > >> So how about we get this patch processed (to fix blk_mq_tagset_busy_iter()), >> as it is independent of blk_mq_queue_tag_busy_iter()? And then wait for some >> update or some more info from Kashyap regarding blk_mq_queue_tag_busy_iter() > Looks fine: > > Reviewed-by: Ming Lei Thanks, I'll just send a v2 with your tag for clarity, as there has been much discussion here. John