[PATCH v5] nvme: multipath: Implemented new iopolicy "queue-depth"
John Meneghini
jmeneghi at redhat.com
Wed May 22 20:00:28 PDT 2024
OK, I've retested this patch and verified the queue-depth policy is working as expected.
Running the same workload using queue-depth policy instead of round-robin provides a more even distribution of IO across all
controllers.
https://github.com/johnmeneghini/iopolicy?tab=readme-ov-file#compare-outstanding-ios-per-controller
And it increases the overall throughput per-namespace:
https://github.com/johnmeneghini/iopolicy?tab=readme-ov-file#compare-outstanding-ios-per-namespace
Tested-by: John Meneghini <jmeneghi at redhat.com>
On 5/22/24 12:54, John Meneghini wrote:
> From: "Ewan D. Milne" <emilne at redhat.com>
>
> The round-robin path selector is inefficient in cases where there is a
> difference in latency between paths. In the presence of one or more
> high latency paths the round-robin selector continues to use the high
> latency path equally. This results in a bias towards the highest latency
> path and can cause a significant decrease in overall performance as IOs
> pile on the highest latency path. This problem is acute with NVMe-oF
> controllers.
>
> The queue-depth policy instead sends I/O requests down the path with the
> least amount of requests in its request queue. Paths with lower latency
> will clear requests more quickly and have less requests in their queues
> compared to higher latency paths. The goal of this path selector is to
> make more use of lower latency paths which will bring down overall IO
> latency and increase throughput and performance.
>
> Signed-off-by: Thomas Song <tsong at purestorage.com>
> [emilne: patch developed by Thomas Song @ Pure Storage, fixed whitespace
> and compilation warnings, updated MODULE_PARM description, and
> fixed potential issue with ->current_path[] being used]
> Signed-off-by: Ewan D. Milne <emilne at redhat.com>
> [jmeneghi: vairious changes and improvements, addressed review comments]
> Signed-off-by: John Meneghini <jmeneghi at redhat.com>
> Link: https://lore.kernel.org/linux-nvme/20240509202929.831680-1-jmeneghi@redhat.com/
> Tested-by: Marco Patalano <mpatalan at redhat.com>
> Reviewed-by: Randy Jennings <randyj at purestorage.com>
> Tested-by: Jyoti Rani <jrani at purestorage.com>
> ---
> drivers/nvme/host/core.c | 2 +-
> drivers/nvme/host/multipath.c | 94 +++++++++++++++++++++++++++++++++--
> drivers/nvme/host/nvme.h | 5 ++
> 3 files changed, 96 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index 7706df237349..66dc676677d4 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -110,7 +110,7 @@ struct workqueue_struct *nvme_delete_wq;
> EXPORT_SYMBOL_GPL(nvme_delete_wq);
>
> static LIST_HEAD(nvme_subsystems);
> -static DEFINE_MUTEX(nvme_subsystems_lock);
> +DEFINE_MUTEX(nvme_subsystems_lock);
>
> static DEFINE_IDA(nvme_instance_ida);
> static dev_t nvme_ctrl_base_chr_devt;
> diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
> index 1bee176fd850..96264c5c979f 100644
> --- a/drivers/nvme/host/multipath.c
> +++ b/drivers/nvme/host/multipath.c
> @@ -17,6 +17,7 @@ MODULE_PARM_DESC(multipath,
> static const char *nvme_iopolicy_names[] = {
> [NVME_IOPOLICY_NUMA] = "numa",
> [NVME_IOPOLICY_RR] = "round-robin",
> + [NVME_IOPOLICY_QD] = "queue-depth",
> };
>
> static int iopolicy = NVME_IOPOLICY_NUMA;
> @@ -29,6 +30,8 @@ static int nvme_set_iopolicy(const char *val, const struct kernel_param *kp)
> iopolicy = NVME_IOPOLICY_NUMA;
> else if (!strncmp(val, "round-robin", 11))
> iopolicy = NVME_IOPOLICY_RR;
> + else if (!strncmp(val, "queue-depth", 11))
> + iopolicy = NVME_IOPOLICY_QD;
> else
> return -EINVAL;
>
> @@ -43,7 +46,7 @@ static int nvme_get_iopolicy(char *buf, const struct kernel_param *kp)
> module_param_call(iopolicy, nvme_set_iopolicy, nvme_get_iopolicy,
> &iopolicy, 0644);
> MODULE_PARM_DESC(iopolicy,
> - "Default multipath I/O policy; 'numa' (default) or 'round-robin'");
> + "Default multipath I/O policy; 'numa' (default), 'round-robin' or 'queue-depth'");
>
> void nvme_mpath_default_iopolicy(struct nvme_subsystem *subsys)
> {
> @@ -128,6 +131,11 @@ void nvme_mpath_start_request(struct request *rq)
> struct nvme_ns *ns = rq->q->queuedata;
> struct gendisk *disk = ns->head->disk;
>
> + if (READ_ONCE(ns->head->subsys->iopolicy) == NVME_IOPOLICY_QD) {
> + atomic_inc(&ns->ctrl->nr_active);
> + nvme_req(rq)->flags |= NVME_MPATH_CNT_ACTIVE;
> + }
> +
> if (!blk_queue_io_stat(disk->queue) || blk_rq_is_passthrough(rq))
> return;
>
> @@ -141,6 +149,9 @@ void nvme_mpath_end_request(struct request *rq)
> {
> struct nvme_ns *ns = rq->q->queuedata;
>
> + if ((nvme_req(rq)->flags & NVME_MPATH_CNT_ACTIVE))
> + atomic_dec_if_positive(&ns->ctrl->nr_active);
> +
> if (!(nvme_req(rq)->flags & NVME_MPATH_IO_STATS))
> return;
> bdev_end_io_acct(ns->head->disk->part0, req_op(rq),
> @@ -332,6 +343,43 @@ static struct nvme_ns *nvme_round_robin_path(struct nvme_ns_head *head,
> return found;
> }
>
> +static struct nvme_ns *nvme_queue_depth_path(struct nvme_ns_head *head)
> +{
> + struct nvme_ns *best_opt = NULL, *best_nonopt = NULL, *ns;
> + unsigned int min_depth_opt = UINT_MAX, min_depth_nonopt = UINT_MAX;
> + unsigned int depth;
> +
> + list_for_each_entry_rcu(ns, &head->list, siblings) {
> + if (nvme_path_is_disabled(ns))
> + continue;
> +
> + depth = atomic_read(&ns->ctrl->nr_active);
> +
> + switch (ns->ana_state) {
> + case NVME_ANA_OPTIMIZED:
> + if (depth < min_depth_opt) {
> + min_depth_opt = depth;
> + best_opt = ns;
> + }
> + break;
> +
> + case NVME_ANA_NONOPTIMIZED:
> + if (depth < min_depth_nonopt) {
> + min_depth_nonopt = depth;
> + best_nonopt = ns;
> + }
> + break;
> + default:
> + break;
> + }
> +
> + if (min_depth_opt == 0)
> + return best_opt;
> + }
> +
> + return best_opt ? best_opt : best_nonopt;
> +}
> +
> static inline bool nvme_path_is_optimized(struct nvme_ns *ns)
> {
> return nvme_ctrl_state(ns->ctrl) == NVME_CTRL_LIVE &&
> @@ -340,15 +388,27 @@ static inline bool nvme_path_is_optimized(struct nvme_ns *ns)
>
> inline struct nvme_ns *nvme_find_path(struct nvme_ns_head *head)
> {
> - int node = numa_node_id();
> + int iopolicy = READ_ONCE(head->subsys->iopolicy);
> + int node;
> struct nvme_ns *ns;
>
> + /*
> + * queue-depth iopolicy does not need to reference ->current_path
> + * but round-robin needs the last path used to advance to the
> + * next one, and numa will continue to use the last path unless
> + * it is or has become not optimized
> + */
> + if (iopolicy == NVME_IOPOLICY_QD)
> + return nvme_queue_depth_path(head);
> +
> + node = numa_node_id();
> ns = srcu_dereference(head->current_path[node], &head->srcu);
> if (unlikely(!ns))
> return __nvme_find_path(head, node);
>
> - if (READ_ONCE(head->subsys->iopolicy) == NVME_IOPOLICY_RR)
> + if (iopolicy == NVME_IOPOLICY_RR)
> return nvme_round_robin_path(head, node, ns);
> +
> if (unlikely(!nvme_path_is_optimized(ns)))
> return __nvme_find_path(head, node);
> return ns;
> @@ -800,6 +860,29 @@ static ssize_t nvme_subsys_iopolicy_show(struct device *dev,
> nvme_iopolicy_names[READ_ONCE(subsys->iopolicy)]);
> }
>
> +static void nvme_subsys_iopolicy_update(struct nvme_subsystem *subsys, int iopolicy)
> +{
> + struct nvme_ctrl *ctrl;
> + int old_iopolicy = READ_ONCE(subsys->iopolicy);
> +
> + if (old_iopolicy == iopolicy)
> + return;
> +
> + WRITE_ONCE(subsys->iopolicy, iopolicy);
> +
> + /* iopolicy changes reset the counters and clear the mpath by design */
> + mutex_lock(&nvme_subsystems_lock);
> + list_for_each_entry(ctrl, &subsys->ctrls, subsys_entry) {
> + atomic_set(&ctrl->nr_active, 0);
> + nvme_mpath_clear_ctrl_paths(ctrl);
> + }
> + mutex_unlock(&nvme_subsystems_lock);
> +
> + pr_notice("%s: changed from %s to %s for subsysnqn %s\n", __func__,
> + nvme_iopolicy_names[old_iopolicy], nvme_iopolicy_names[iopolicy],
> + subsys->subnqn);
> +}
> +
> static ssize_t nvme_subsys_iopolicy_store(struct device *dev,
> struct device_attribute *attr, const char *buf, size_t count)
> {
> @@ -809,7 +892,7 @@ static ssize_t nvme_subsys_iopolicy_store(struct device *dev,
>
> for (i = 0; i < ARRAY_SIZE(nvme_iopolicy_names); i++) {
> if (sysfs_streq(buf, nvme_iopolicy_names[i])) {
> - WRITE_ONCE(subsys->iopolicy, i);
> + nvme_subsys_iopolicy_update(subsys, i);
> return count;
> }
> }
> @@ -920,6 +1003,9 @@ int nvme_mpath_init_identify(struct nvme_ctrl *ctrl, struct nvme_id_ctrl *id)
> !(ctrl->subsys->cmic & NVME_CTRL_CMIC_ANA))
> return 0;
>
> + /* initialize this in the identify path to cover controller resets */
> + atomic_set(&ctrl->nr_active, 0);
> +
> if (!ctrl->max_namespaces ||
> ctrl->max_namespaces > le32_to_cpu(id->nn)) {
> dev_err(ctrl->device,
> diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
> index fc31bd340a63..fa3833d88a85 100644
> --- a/drivers/nvme/host/nvme.h
> +++ b/drivers/nvme/host/nvme.h
> @@ -50,6 +50,8 @@ extern struct workqueue_struct *nvme_wq;
> extern struct workqueue_struct *nvme_reset_wq;
> extern struct workqueue_struct *nvme_delete_wq;
>
> +extern struct mutex nvme_subsystems_lock;
> +
> /*
> * List of workarounds for devices that required behavior not specified in
> * the standard.
> @@ -195,6 +197,7 @@ enum {
> NVME_REQ_CANCELLED = (1 << 0),
> NVME_REQ_USERCMD = (1 << 1),
> NVME_MPATH_IO_STATS = (1 << 2),
> + NVME_MPATH_CNT_ACTIVE = (1 << 3),
> };
>
> static inline struct nvme_request *nvme_req(struct request *req)
> @@ -359,6 +362,7 @@ struct nvme_ctrl {
> size_t ana_log_size;
> struct timer_list anatt_timer;
> struct work_struct ana_work;
> + atomic_t nr_active;
> #endif
>
> #ifdef CONFIG_NVME_HOST_AUTH
> @@ -407,6 +411,7 @@ static inline enum nvme_ctrl_state nvme_ctrl_state(struct nvme_ctrl *ctrl)
> enum nvme_iopolicy {
> NVME_IOPOLICY_NUMA,
> NVME_IOPOLICY_RR,
> + NVME_IOPOLICY_QD,
> };
>
> struct nvme_subsystem {
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