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nvme: export I/O requeue count when no path is usable via sysfs

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When the NVMe namespace head determines that there is no currently
available path to handle I/O (for example, while a controller is
resetting/connecting or due to a transient link failure), incoming
I/Os are added to the requeue list.

Currently, there is no visibility into how many I/Os have been requeued
in this situation. Add a new ns-head sysfs counter
io_requeue_no_usable_path_count, under diag attribute group to expose
the number of I/Os that were requeued due to the absence of an available
path. This counter is also writable thus allowing user to reset it, if
needed.

This statistic can help users understand I/O slowdowns or stalls caused
by temporary path unavailability, and can be consumed by monitoring
tools such as nvme-top for real-time observability.

Tested-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Signed-off-by: Nilay Shroff <nilay@linux.ibm.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>
This commit is contained in:
Nilay Shroff 2026-05-17 00:06:52 +05:30 committed by Keith Busch
parent 30ab37a128
commit 76b5e1591e
3 changed files with 37 additions and 0 deletions
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30
drivers/nvme/host/multipath.c
View File

@ -538,6 +538,7 @@ static void nvme_ns_head_submit_bio(struct bio *bio)
spin_lock_irq(&head->requeue_lock);
bio_list_add(&head->requeue_list, bio);
spin_unlock_irq(&head->requeue_lock);
atomic_long_inc(&head->io_requeue_no_usable_path_count);
} else {
dev_warn_ratelimited(dev, "no available path - failing I/O\n");
@ -1192,6 +1193,35 @@ static ssize_t multipath_failover_count_store(struct device *dev,
DEVICE_ATTR_RW(multipath_failover_count);
static ssize_t io_requeue_no_usable_path_count_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
struct gendisk *disk = dev_to_disk(dev);
struct nvme_ns_head *head = disk->private_data;
return sysfs_emit(buf, "%lu\n",
atomic_long_read(&head->io_requeue_no_usable_path_count));
}
static ssize_t io_requeue_no_usable_path_count_store(struct device *dev,
struct device_attribute *attr, const char *buf, size_t count)
{
int err;
unsigned long requeue_cnt;
struct gendisk *disk = dev_to_disk(dev);
struct nvme_ns_head *head = disk->private_data;
err = kstrtoul(buf, 0, &requeue_cnt);
if (err)
return -EINVAL;
atomic_long_set(&head->io_requeue_no_usable_path_count, requeue_cnt);
return count;
}
DEVICE_ATTR_RW(io_requeue_no_usable_path_count);
static int nvme_lookup_ana_group_desc(struct nvme_ctrl *ctrl,
struct nvme_ana_group_desc *desc, void *data)
{

2
drivers/nvme/host/nvme.h
View File

@ -566,6 +566,7 @@ struct nvme_ns_head {
unsigned long flags;
struct delayed_work remove_work;
unsigned int delayed_removal_secs;
atomic_long_t io_requeue_no_usable_path_count;
#define NVME_NSHEAD_DISK_LIVE 0
#define NVME_NSHEAD_QUEUE_IF_NO_PATH 1
struct nvme_ns __rcu *current_path[];
@ -1069,6 +1070,7 @@ extern struct device_attribute dev_attr_queue_depth;
extern struct device_attribute dev_attr_numa_nodes;
extern struct device_attribute dev_attr_delayed_removal_secs;
extern struct device_attribute dev_attr_multipath_failover_count;
extern struct device_attribute dev_attr_io_requeue_no_usable_path_count;
extern struct device_attribute subsys_attr_iopolicy;
static inline bool nvme_disk_is_ns_head(struct gendisk *disk)

5
drivers/nvme/host/sysfs.c
View File

@ -403,6 +403,7 @@ static struct attribute *nvme_ns_diag_attrs[] = {
&dev_attr_io_errors.attr,
#ifdef CONFIG_NVME_MULTIPATH
&dev_attr_multipath_failover_count.attr,
&dev_attr_io_requeue_no_usable_path_count.attr,
#endif
NULL,
};
@ -427,6 +428,10 @@ static umode_t nvme_ns_diag_attrs_are_visible(struct kobject *kobj,
if (nvme_disk_is_ns_head(dev_to_disk(dev)))
return 0;
}
if (a == &dev_attr_io_requeue_no_usable_path_count.attr) {
if (!nvme_disk_is_ns_head(dev_to_disk(dev)))
return 0;
}
#endif
return a->mode;
}