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Date: Mon, 18 Oct 2021 10:33:47 +0100 From: John Garry <john.garry@...wei.com> To: Ming Lei <ming.lei@...hat.com> CC: "axboe@...nel.dk" <axboe@...nel.dk>, "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "kashyap.desai@...adcom.com" <kashyap.desai@...adcom.com>, "hare@...e.de" <hare@...e.de> Subject: Re: [PATCH] blk-mq: Fix blk_mq_tagset_busy_iter() for shared tags 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<ming.lei@...hat.com> Thanks, I'll just send a v2 with your tag for clarity, as there has been much discussion here. John
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