[PATCH V6 0/3] blk-mq: fix blk_mq_alloc_request_hctx

[PATCH V6 0/3] blk-mq: fix blk_mq_alloc_request_hctx

[Ming Lei]

Hi,

blk_mq_alloc_request_hctx() is used by NVMe fc/rdma/tcp/loop to connect
io queue. Also the sw ctx is chosen as the 1st online cpu in hctx->cpumask.
However, all cpus in hctx->cpumask may be offline.

This usage model isn't well supported by blk-mq which supposes allocator is
always done on one online CPU in hctx->cpumask. This assumption is
related with managed irq, which also requires blk-mq to drain inflight
request in this hctx when the last cpu in hctx->cpumask is going to
offline.

However, NVMe fc/rdma/tcp/loop don't use managed irq, so we should allow
them to ask for request allocation when the specified hctx is inactive
(all cpus in hctx->cpumask are offline). Fix blk_mq_alloc_request_hctx() by
allowing to allocate request when all CPUs of this hctx are offline.

Wen Xiong has verified V4 in her nvmef test.

V6:
	- move device_has_managed_msi_irq() into kernel/irq/msi.c

V5:
	- take John Garry's suggestion to replace device field with
	new helper of device_has_managed_msi_irq()
V4:
	- remove patches for cleanup queue map helpers
	- take Christoph's suggestion to add field into 'struct device' for
	describing if managed irq is allocated from one device

V3:
	- cleanup map queues helpers, and remove pci/virtio/rdma queue
	  helpers
	- store use managed irq info into qmap

V2:
	- use flag of BLK_MQ_F_MANAGED_IRQ
	- pass BLK_MQ_F_MANAGED_IRQ from driver explicitly
	- kill BLK_MQ_F_STACKING


Ming Lei (3):
  genirq: add device_has_managed_msi_irq
  blk-mq: mark if one queue map uses managed irq
  blk-mq: don't deactivate hctx if managed irq isn't used

 block/blk-mq-pci.c                     |  2 ++
 block/blk-mq-rdma.c                    |  7 +++++++
 block/blk-mq-virtio.c                  |  2 ++
 block/blk-mq.c                         | 27 ++++++++++++++++----------
 block/blk-mq.h                         |  8 ++++++++
 drivers/scsi/hisi_sas/hisi_sas_v2_hw.c |  1 +
 include/linux/blk-mq.h                 |  3 ++-
 include/linux/msi.h                    |  5 +++++
 kernel/irq/msi.c                       | 18 +++++++++++++++++
 9 files changed, 62 insertions(+), 11 deletions(-)

-- 
2.31.1

[PATCH V6 1/3] genirq: add device_has_managed_msi_irq

[Ming Lei]

irq vector allocation with managed affinity may be used by driver, and
blk-mq needs this info for draining queue because genirq core will shutdown
managed irq when all CPUs in the affinity mask are offline.

The info of using managed irq is often produced by drivers, and it is
consumed by blk-mq, so different subsystems are involved in this info flow.

Address this issue by adding one helper of device_has_managed_msi_irq()
which is suggested by John Garry.

Suggested-by: John Garry <john.garry@huawei.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 include/linux/msi.h |  5 +++++
 kernel/irq/msi.c    | 18 ++++++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/include/linux/msi.h b/include/linux/msi.h
index 6aff469e511d..2d0f3962d3c3 100644
--- a/include/linux/msi.h
+++ b/include/linux/msi.h
@@ -59,10 +59,15 @@ struct platform_msi_priv_data;
 void __get_cached_msi_msg(struct msi_desc *entry, struct msi_msg *msg);
 #ifdef CONFIG_GENERIC_MSI_IRQ
 void get_cached_msi_msg(unsigned int irq, struct msi_msg *msg);
+bool device_has_managed_msi_irq(struct device *dev);
 #else
 static inline void get_cached_msi_msg(unsigned int irq, struct msi_msg *msg)
 {
 }
+static inline bool device_has_managed_msi_irq(struct device *dev)
+{
+	return false;
+}
 #endif
 
 typedef void (*irq_write_msi_msg_t)(struct msi_desc *desc,
diff --git a/kernel/irq/msi.c b/kernel/irq/msi.c
index c41965e348b5..01aae22246c8 100644
--- a/kernel/irq/msi.c
+++ b/kernel/irq/msi.c
@@ -69,6 +69,24 @@ void get_cached_msi_msg(unsigned int irq, struct msi_msg *msg)
 }
 EXPORT_SYMBOL_GPL(get_cached_msi_msg);
 
+/**
+ * device_has_managed_msi_irq - Query if device has managed irq entry
+ * @dev:	Pointer to the device for which we want to query
+ *
+ * Return true if there is managed irq vector allocated on this device
+ */
+bool device_has_managed_msi_irq(struct device *dev)
+{
+	struct msi_desc *desc;
+
+	for_each_msi_entry(desc, dev) {
+		if (desc->affinity && desc->affinity->is_managed)
+			return true;
+	}
+	return false;
+}
+EXPORT_SYMBOL_GPL(device_has_managed_msi_irq);
+
 #ifdef CONFIG_GENERIC_MSI_IRQ_DOMAIN
 static inline void irq_chip_write_msi_msg(struct irq_data *data,
 					  struct msi_msg *msg)
-- 
2.31.1

[PATCH V6 2/3] blk-mq: mark if one queue map uses managed irq

[Ming Lei]

Retrieve this info via new added helper of device_has_managed_msi_irq,
then we can decide if one hctx needs to be drained before all its CPUs
become offline.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: John Garry <john.garry@huawei.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk-mq-pci.c                     | 2 ++
 block/blk-mq-rdma.c                    | 7 +++++++
 block/blk-mq-virtio.c                  | 2 ++
 drivers/scsi/hisi_sas/hisi_sas_v2_hw.c | 1 +
 include/linux/blk-mq.h                 | 3 ++-
 5 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/block/blk-mq-pci.c b/block/blk-mq-pci.c
index b595a94c4d16..e452cda0896a 100644
--- a/block/blk-mq-pci.c
+++ b/block/blk-mq-pci.c
@@ -8,6 +8,7 @@
 #include <linux/blk-mq-pci.h>
 #include <linux/pci.h>
 #include <linux/module.h>
+#include <linux/msi.h>
 
 #include "blk-mq.h"
 
@@ -37,6 +38,7 @@ int blk_mq_pci_map_queues(struct blk_mq_queue_map *qmap, struct pci_dev *pdev,
 		for_each_cpu(cpu, mask)
 			qmap->mq_map[cpu] = qmap->queue_offset + queue;
 	}
+	qmap->use_managed_irq = device_has_managed_msi_irq(&pdev->dev);
 
 	return 0;
 
diff --git a/block/blk-mq-rdma.c b/block/blk-mq-rdma.c
index 14f968e58b8f..19ad31c44eab 100644
--- a/block/blk-mq-rdma.c
+++ b/block/blk-mq-rdma.c
@@ -36,6 +36,13 @@ int blk_mq_rdma_map_queues(struct blk_mq_queue_map *map,
 			map->mq_map[cpu] = map->queue_offset + queue;
 	}
 
+	/*
+	 * RDMA doesn't use managed irq, and nvme rdma driver can allocate
+	 * and submit requests on specified hctx via
+	 * blk_mq_alloc_request_hctx
+	 */
+	map->use_managed_irq = false;
+
 	return 0;
 
 fallback:
diff --git a/block/blk-mq-virtio.c b/block/blk-mq-virtio.c
index 7b8a42c35102..2ce39fb77dce 100644
--- a/block/blk-mq-virtio.c
+++ b/block/blk-mq-virtio.c
@@ -7,6 +7,7 @@
 #include <linux/blk-mq-virtio.h>
 #include <linux/virtio_config.h>
 #include <linux/module.h>
+#include <linux/msi.h>
 #include "blk-mq.h"
 
 /**
@@ -38,6 +39,7 @@ int blk_mq_virtio_map_queues(struct blk_mq_queue_map *qmap,
 		for_each_cpu(cpu, mask)
 			qmap->mq_map[cpu] = qmap->queue_offset + queue;
 	}
+	qmap->use_managed_irq = device_has_managed_msi_irq(&vdev->dev);
 
 	return 0;
 fallback:
diff --git a/drivers/scsi/hisi_sas/hisi_sas_v2_hw.c b/drivers/scsi/hisi_sas/hisi_sas_v2_hw.c
index b0b2361e63fe..7d7df261d346 100644
--- a/drivers/scsi/hisi_sas/hisi_sas_v2_hw.c
+++ b/drivers/scsi/hisi_sas/hisi_sas_v2_hw.c
@@ -3562,6 +3562,7 @@ static int map_queues_v2_hw(struct Scsi_Host *shost)
 		for_each_cpu(cpu, mask)
 			qmap->mq_map[cpu] = qmap->queue_offset + queue;
 	}
+	qmap->use_managed_irq = true;
 
 	return 0;
 
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 1d18447ebebc..d54a795ec971 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -192,7 +192,8 @@ struct blk_mq_hw_ctx {
 struct blk_mq_queue_map {
 	unsigned int *mq_map;
 	unsigned int nr_queues;
-	unsigned int queue_offset;
+	unsigned int queue_offset:31;
+	unsigned int use_managed_irq:1;
 };
 
 /**
-- 
2.31.1

[PATCH V6 3/3] blk-mq: don't deactivate hctx if managed irq isn't used

[Ming Lei]

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.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk-mq.c | 27 +++++++++++++++++----------
 block/blk-mq.h |  8 ++++++++
 2 files changed, 25 insertions(+), 10 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 2c4ac51e54eb..591ab07c64d8 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -427,6 +427,15 @@ struct request *blk_mq_alloc_request(struct request_queue *q, unsigned int op,
 }
 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;
+}
+
 struct request *blk_mq_alloc_request_hctx(struct request_queue *q,
 	unsigned int op, blk_mq_req_flags_t flags, unsigned int hctx_idx)
 {
@@ -468,7 +477,10 @@ struct request *blk_mq_alloc_request_hctx(struct request_queue *q,
 	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)
@@ -1501,15 +1513,6 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)
 	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.
@@ -2556,6 +2559,10 @@ static int blk_mq_hctx_notify_offline(unsigned int cpu, struct hlist_node *node)
 	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;
diff --git a/block/blk-mq.h b/block/blk-mq.h
index d08779f77a26..7333b659d8f5 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -119,6 +119,14 @@ static inline struct blk_mq_hw_ctx *blk_mq_map_queue(struct request_queue *q,
 	return ctx->hctxs[type];
 }
 
+static inline 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;
+}
+
 /*
  * sysfs helpers
  */
-- 
2.31.1

Re: [PATCH V6 1/3] genirq: add device_has_managed_msi_irq

[Christoph Hellwig]

On Thu, Jul 22, 2021 at 05:52:44PM +0800, Ming Lei wrote:
> irq vector allocation with managed affinity may be used by driver, and
> blk-mq needs this info for draining queue because genirq core will shutdown
> managed irq when all CPUs in the affinity mask are offline.
> 
> The info of using managed irq is often produced by drivers, and it is
> consumed by blk-mq, so different subsystems are involved in this info flow.
> 
> Address this issue by adding one helper of device_has_managed_msi_irq()
> which is suggested by John Garry.

This implies non-MSI irqs can't be managed, which is true right now.
If the irq maintaines are fine with that:

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH V6 2/3] blk-mq: mark if one queue map uses managed irq

[Christoph Hellwig]

On Thu, Jul 22, 2021 at 05:52:45PM +0800, Ming Lei wrote:
	 and nvme rdma driver can allocate
> +	 * and submit requests on specified hctx via
> +	 * blk_mq_alloc_request_hctx

Why does that matter for this setting?

Re: [PATCH V6 0/3] blk-mq: fix blk_mq_alloc_request_hctx

[Daniel Wagner]

On Thu, Jul 22, 2021 at 05:52:43PM +0800, Ming Lei wrote:
> Wen Xiong has verified V4 in her nvmef test.

FWIW, I am testing this series right now. I observe hanging I/Os
again, but I am not totally sure if my test setup is working
properly. Working on it. I'll keep you posted.

Re: [PATCH V6 2/3] blk-mq: mark if one queue map uses managed irq

[Ming Lei]

On Thu, Jul 22, 2021 at 03:06:09PM +0200, Christoph Hellwig wrote:
> On Thu, Jul 22, 2021 at 05:52:45PM +0800, Ming Lei wrote:
> 	 and nvme rdma driver can allocate
> > +	 * and submit requests on specified hctx via
> > +	 * blk_mq_alloc_request_hctx
> 
> Why does that matter for this setting?

blk_mq_alloc_request_hctx() has been broken for long time, which
can only work if the hctx isn't driven by non-managed irq.


Thanks,
Ming

Re: [PATCH V6 2/3] blk-mq: mark if one queue map uses managed irq

[Christoph Hellwig]

On Thu, Jul 22, 2021 at 11:40:19PM +0800, Ming Lei wrote:
> On Thu, Jul 22, 2021 at 03:06:09PM +0200, Christoph Hellwig wrote:
> > On Thu, Jul 22, 2021 at 05:52:45PM +0800, Ming Lei wrote:
> > 	 and nvme rdma driver can allocate
> > > +	 * and submit requests on specified hctx via
> > > +	 * blk_mq_alloc_request_hctx
> > 
> > Why does that matter for this setting?
> 
> blk_mq_alloc_request_hctx() has been broken for long time, which
> can only work if the hctx isn't driven by non-managed irq.

The qla2xxx and lpfc drivers uses managed interrupt.  I'm not quite
sure if the nvme-fc queues directly map to those interrupts, though.

Re: [PATCH V6 0/3] blk-mq: fix blk_mq_alloc_request_hctx

[Ming Lei]

On Thu, Jul 22, 2021 at 10:06:51PM +0000, Wen Xiong wrote:
>    > Wen Xiong has verified V4 in her nvmef test.
> 
>    >>FWIW, I am testing this series right now. I observe hanging I/Os
>    >>again, but I am not totally sure if my test setup is working
>    >>properly. Working on it. I'll keep you posted.
>     
> 
>  I built the latest upstream(v5.14-rc2) + Ming's V6 + Daniel's V3: didn't work.
> 

Hi Wenxiong,

V6 is basically same with V4, can you figure out where the failure
comes?(v5.14-rc2, V6 or Daniel's V3) 

I verified that V6 works as expected by tracing blk_mq_update_queue_map():

#!/usr/bin/bpftrace
#include <linux/blk-mq.h>
kprobe:blk_mq_update_queue_map
{
	@in_map[tid]=1;
	@set[tid] = (struct blk_mq_tag_set *)arg0;
	@ms[tid] = kstack;
}

kretprobe:blk_mq_update_queue_map
/@in_map[tid]==1/
{
	$s = @set[tid];
	$m = (struct blk_mq_queue_map *)$s->map;

	printf("%s %d: %s queues %d use_managed_irq %d\n",
		comm, pid, @ms[tid], $s->nr_hw_queues, $m->use_managed_irq);
}


Thanks,
Ming

Re: [PATCH V6 0/3] blk-mq: fix blk_mq_alloc_request_hctx

[Daniel Wagner]

Hi,

On Mon, Jul 26, 2021 at 02:14:30PM +0000, Wen Xiong wrote:
> >>V6 is basically same with V4, can you figure out where the failure
> >>comes?(v5.14-rc2, V6 or Daniel's V3)
>  
> Looks 3/3 was not patched cleanly in v5.14-rc2 last week.  I made the changes
> in block/blk-mq.c.rej manually but still missed the last part of 3/3 patch.

Sorry for the long delay on my side. It took a while to get my test
setup running again. The qla2xxx driver really doesn't like 'fast'
remote port toggling. But that's a different story.

Anyway, it turns out that my patch series is still not working
correctly. When I tested the series I deliberate forced to execute
the 'revising io queue count' path in nvme_fc_recreate_io_queues by
doing:

--- a/drivers/nvme/host/fc.c
+++ b/drivers/nvme/host/fc.c
@@ -2954,7 +2954,7 @@ nvme_fc_recreate_io_queues(struct nvme_fc_ctrl *ctrl)
        if (ctrl->ctrl.queue_count == 1)
                return 0;
 
-       if (prior_ioq_cnt != nr_io_queues) {
+       if (prior_ioq_cnt != nr_io_queues - 1) {
                dev_info(ctrl->ctrl.device,
                        "reconnect: revising io queue count from %d to %d\n",
                        prior_ioq_cnt, nr_io_queues);


With this change I can't observe any I/O hanging. Without the change it
hangs in the first iteration.

In Wen's setup we observed in earlier debugging sessions that the
nr_io_queues does change. So this explains why Wen doesn't see any
hanging I/Os.

@James, I think we need to look at bit more at the freeze code. BTW,
my initial patch which just added a nvme_start_freeze() in
nvme_fc_delete_association() doesn't work either for the 'prior_ioq_cnt
== nr_io_queues' case.

So I think Ming series can be merged as the hanging I/Os are clearly not
caused by the series.

Feel free to add

Tested-by: Daniel Wagner <dwagner@suse.de>

Thanks,
Daniel

Re: [PATCH V6 0/3] blk-mq: fix blk_mq_alloc_request_hctx

[Daniel Wagner]

Any chance to queue this series?

Re: [PATCH V6 3/3] blk-mq: don't deactivate hctx if managed irq isn't used

[John Garry]

On 22/07/2021 10:52, Ming Lei wrote:
> 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.
> 
> Reviewed-by: Christoph Hellwig<hch@lst.de>
> Signed-off-by: Ming Lei<ming.lei@redhat.com>

Sorry for lateness. Just a few minor comments below, regardless:

Reviewed-by: John Garry <john.garry@huawei.com>

> ---
>   block/blk-mq.c | 27 +++++++++++++++++----------
>   block/blk-mq.h |  8 ++++++++
>   2 files changed, 25 insertions(+), 10 deletions(-)
> 
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 2c4ac51e54eb..591ab07c64d8 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -427,6 +427,15 @@ struct request *blk_mq_alloc_request(struct request_queue *q, unsigned int op,
>   }
>   EXPORT_SYMBOL(blk_mq_alloc_request);
>   
> +static inline int blk_mq_first_mapped_cpu(struct blk_mq_hw_ctx *hctx)

I don't see why it needs to be inline. I think generally we leave it to 
the compiler to decide.

> +{
> +	int cpu = cpumask_first_and(hctx->cpumask, cpu_online_mask);
> +
> +	if (cpu >= nr_cpu_ids)
> +		cpu = cpumask_first(hctx->cpumask);
> +	return cpu;
> +}
> +
>   struct request *blk_mq_alloc_request_hctx(struct request_queue *q,
>   	unsigned int op, blk_mq_req_flags_t flags, unsigned int hctx_idx)
>   {
> @@ -468,7 +477,10 @@ struct request *blk_mq_alloc_request_hctx(struct request_queue *q,
>   	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)
> @@ -1501,15 +1513,6 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)
>   	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.
> @@ -2556,6 +2559,10 @@ static int blk_mq_hctx_notify_offline(unsigned int cpu, struct hlist_node *node)
>   	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;

In a previous version (v2) I think that we just didn't register the cpu 
hotplug handlers, so not sure why that changed.

> +
>   	if (!cpumask_test_cpu(cpu, hctx->cpumask) ||
>   	    !blk_mq_last_cpu_in_hctx(cpu, hctx))
>   		return 0;
> diff --git a/block/blk-mq.h b/block/blk-mq.h
> index d08779f77a26..7333b659d8f5 100644
> --- a/block/blk-mq.h
> +++ b/block/blk-mq.h
> @@ -119,6 +119,14 @@ static inline struct blk_mq_hw_ctx *blk_mq_map_queue(struct request_queue *q,
>   	return ctx->hctxs[type];
>   }
>   
> +static inline 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;
> +}

This function only seems to be used in blk-mq.c, so not sure why you put 
it in .h file.

Re: [PATCH V6 3/3] blk-mq: don't deactivate hctx if managed irq isn't used

[Ming Lei]

On Wed, Aug 18, 2021 at 10:38:15AM +0100, John Garry wrote:
> On 22/07/2021 10:52, Ming Lei wrote:
> > 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.
> > 
> > Reviewed-by: Christoph Hellwig<hch@lst.de>
> > Signed-off-by: Ming Lei<ming.lei@redhat.com>
> 
> Sorry for lateness. Just a few minor comments below, regardless:
> 
> Reviewed-by: John Garry <john.garry@huawei.com>
> 
> > ---
> >   block/blk-mq.c | 27 +++++++++++++++++----------
> >   block/blk-mq.h |  8 ++++++++
> >   2 files changed, 25 insertions(+), 10 deletions(-)
> > 
> > diff --git a/block/blk-mq.c b/block/blk-mq.c
> > index 2c4ac51e54eb..591ab07c64d8 100644
> > --- a/block/blk-mq.c
> > +++ b/block/blk-mq.c
> > @@ -427,6 +427,15 @@ struct request *blk_mq_alloc_request(struct request_queue *q, unsigned int op,
> >   }
> >   EXPORT_SYMBOL(blk_mq_alloc_request);
> > +static inline int blk_mq_first_mapped_cpu(struct blk_mq_hw_ctx *hctx)
> 
> I don't see why it needs to be inline. I think generally we leave it to the
> compiler to decide.

Usually if one function is called more than two times, it will not be
inlined. blk_mq_first_mapped_cpu() is called in fast path, so we need to
inline it.

> 
> > +{
> > +	int cpu = cpumask_first_and(hctx->cpumask, cpu_online_mask);
> > +
> > +	if (cpu >= nr_cpu_ids)
> > +		cpu = cpumask_first(hctx->cpumask);
> > +	return cpu;
> > +}
> > +
> >   struct request *blk_mq_alloc_request_hctx(struct request_queue *q,
> >   	unsigned int op, blk_mq_req_flags_t flags, unsigned int hctx_idx)
> >   {
> > @@ -468,7 +477,10 @@ struct request *blk_mq_alloc_request_hctx(struct request_queue *q,
> >   	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)
> > @@ -1501,15 +1513,6 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)
> >   	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.
> > @@ -2556,6 +2559,10 @@ static int blk_mq_hctx_notify_offline(unsigned int cpu, struct hlist_node *node)
> >   	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;
> 
> In a previous version (v2) I think that we just didn't register the cpu
> hotplug handlers, so not sure why that changed.

Sorry, forget to mention the change, inside blk_mq_realloc_hw_ctxs()
we may grab one cached hctx without initializing it, so use managed irq
info change may not be visible in blk_mq_init_hctx().

Given blk_mq_hctx_notify_offline() isn't in fast path, I'd rather to
check in blk_mq_hctx_notify_offline(), which is more reliable than
running the check in blk_mq_init_hctx().

> 
> > +
> >   	if (!cpumask_test_cpu(cpu, hctx->cpumask) ||
> >   	    !blk_mq_last_cpu_in_hctx(cpu, hctx))
> >   		return 0;
> > diff --git a/block/blk-mq.h b/block/blk-mq.h
> > index d08779f77a26..7333b659d8f5 100644
> > --- a/block/blk-mq.h
> > +++ b/block/blk-mq.h
> > @@ -119,6 +119,14 @@ static inline struct blk_mq_hw_ctx *blk_mq_map_queue(struct request_queue *q,
> >   	return ctx->hctxs[type];
> >   }
> > +static inline 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;
> > +}
> 
> This function only seems to be used in blk-mq.c, so not sure why you put it
> in .h file.

oops, the helper must be used in early version, I will send a new
version soon.


Thanks,
Ming