From: Ming Lei <ming.lei@redhat.com>
Date: Wed, 18 Aug 2021 22:44:28 +0800
Subject: blk-mq: don't deactivate hctx if managed irq isn't used
Patch-mainline: Not yet, https://lore.kernel.org/linux-block/20210818144428.896216-1-ming.lei@redhat.com/
References: bsc#1185762

blk-mq deactivates one hctx when the last CPU in hctx->cpumask become
offline by draining all requests originated from this hctx and moving new
allocation to other active hctx. This way is for avoiding inflight IO in
case of managed irq because managed irq is shutdown when the last CPU in
the irq's affinity becomes offline.

However, lots of drivers(nvme fc, rdma, tcp, loop, ...) don't use managed
irq, so they needn't to deactivate hctx when the last CPU becomes offline.
Also, some of them are the only user of blk_mq_alloc_request_hctx() which
is used for connecting io queue. And their requirement is that the connect
request needs to be submitted successfully via one specified hctx even
though all CPUs in this hctx->cpumask have become offline.

Addressing the requirement for nvme fc/rdma/loop by allowing to
allocate request from one hctx when all CPUs in this hctx are offline,
since these drivers don't use managed irq.

Finally don't deactivate one hctx when it doesn't use managed irq.

Tested-by: Wen Xiong <wenxiong@us.ibm.com>
Reviewed-by: John Garry <john.garry@huawei.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Acked-by: Daniel Wagner <dwagner@suse.de>
---
 block/blk-mq.c |   35 +++++++++++++++++++++++++----------
 1 file changed, 25 insertions(+), 10 deletions(-)

--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -424,6 +424,23 @@ struct request *blk_mq_alloc_request(str
 }
 EXPORT_SYMBOL(blk_mq_alloc_request);
 
+static inline int blk_mq_first_mapped_cpu(struct blk_mq_hw_ctx *hctx)
+{
+	int cpu = cpumask_first_and(hctx->cpumask, cpu_online_mask);
+
+	if (cpu >= nr_cpu_ids)
+		cpu = cpumask_first(hctx->cpumask);
+	return cpu;
+}
+
+static bool blk_mq_hctx_use_managed_irq(struct blk_mq_hw_ctx *hctx)
+{
+	if (hctx->type == HCTX_TYPE_POLL)
+		return false;
+
+	return hctx->queue->tag_set->map[hctx->type].use_managed_irq;
+}
+
 struct request *blk_mq_alloc_request_hctx(struct request_queue *q,
 	unsigned int op, blk_mq_req_flags_t flags, unsigned int hctx_idx)
 {
@@ -465,7 +482,10 @@ struct request *blk_mq_alloc_request_hct
 	data.hctx = q->queue_hw_ctx[hctx_idx];
 	if (!blk_mq_hw_queue_mapped(data.hctx))
 		goto out_queue_exit;
-	cpu = cpumask_first_and(data.hctx->cpumask, cpu_online_mask);
+
+	WARN_ON_ONCE(blk_mq_hctx_use_managed_irq(data.hctx));
+
+	cpu = blk_mq_first_mapped_cpu(data.hctx);
 	data.ctx = __blk_mq_get_ctx(q, cpu);
 
 	if (!q->elevator)
@@ -1507,15 +1527,6 @@ static void __blk_mq_run_hw_queue(struct
 	hctx_unlock(hctx, srcu_idx);
 }
 
-static inline int blk_mq_first_mapped_cpu(struct blk_mq_hw_ctx *hctx)
-{
-	int cpu = cpumask_first_and(hctx->cpumask, cpu_online_mask);
-
-	if (cpu >= nr_cpu_ids)
-		cpu = cpumask_first(hctx->cpumask);
-	return cpu;
-}
-
 /*
  * It'd be great if the workqueue API had a way to pass
  * in a mask and had some smarts for more clever placement.
@@ -2457,6 +2468,10 @@ static int blk_mq_hctx_notify_offline(un
 	struct blk_mq_hw_ctx *hctx = hlist_entry_safe(node,
 			struct blk_mq_hw_ctx, cpuhp_online);
 
+	/* hctx needn't to be deactivated in case managed irq isn't used */
+	if (!blk_mq_hctx_use_managed_irq(hctx))
+		return 0;
+
 	if (!cpumask_test_cpu(cpu, hctx->cpumask) ||
 	    !blk_mq_last_cpu_in_hctx(cpu, hctx))
 		return 0;