Re: [PATCH v3 1/1] nvme: multipath: Implemented new iopolicy "queue-depth"
From: Nilay Shroff
Date: Tue May 21 2024 - 04:48:56 EST
On 5/21/24 01:50, John Meneghini wrote:
> From: "Ewan D. Milne" <emilne@xxxxxxxxxx>
>
> The round-robin path selector is inefficient in cases where there is a
> difference in latency between multiple active optimized paths. In the
> presence of one or more high latency paths the round-robin selector
> continues to the high latency path equally. This results in a bias
> towards the highest latency path and can cause is significant decrease
> in overall performance as IOs pile on the lowest latency path. This
> problem is particularly accute 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.
>
> Signed-off-by: Ewan D. Milne <emilne@xxxxxxxxxx>
> [tsong: 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: Thomas Song <tsong@xxxxxxxxxxxxxxx>
> [jmeneghi: vairious changes and improvements, addressed review comments]
> Signed-off-by: John Meneghini <jmeneghi@xxxxxxxxxx>
> Link: https://lore.kernel.org/linux-nvme/20240509202929.831680-1-jmeneghi@xxxxxxxxxx/
> Tested-by: Marco Patalano <mpatalan@xxxxxxxxxx>
> Reviewed-by: Randy Jennings <randyj@xxxxxxxxxx>
> Tested-by: Jyoti Rani <jani@xxxxxxxxxxxxxxx>
> ---
> drivers/nvme/host/core.c | 2 +-
> drivers/nvme/host/multipath.c | 86 +++++++++++++++++++++++++++++++++--
> drivers/nvme/host/nvme.h | 9 ++++
> 3 files changed, 92 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index a066429b790d..1dd7c52293ff 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 5397fb428b24..0e2b6e720e95 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)
> {
> @@ -127,6 +130,11 @@ 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;
>
> @@ -140,8 +148,12 @@ 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),
> blk_rq_bytes(rq) >> SECTOR_SHIFT,
> nvme_req(rq)->start_time);
> @@ -330,6 +342,40 @@ static struct nvme_ns *nvme_round_robin_path(struct nvme_ns_head *head,
> return found;
> }
>
I think you may also want to reset nr_active counter if in case, in-flight nvme request
is cancelled. If the request is cancelled then nvme_mpath_end_request() wouldn't be invoked.
So you may want to reset nr_active counter from nvme_cancel_request() as below:
diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index bf7615cb36ee..4fea7883ce8e 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -497,8 +497,9 @@ EXPORT_SYMBOL_GPL(nvme_host_path_error);
bool nvme_cancel_request(struct request *req, void *data)
{
- dev_dbg_ratelimited(((struct nvme_ctrl *) data)->device,
- "Cancelling I/O %d", req->tag);
+ struct nvme_ctrl *ctrl = (struct nvme_ctrl *)data;
+
+ dev_dbg_ratelimited(ctrl->device, "Cancelling I/O %d", req->tag);
/* don't abort one completed or idle request */
if (blk_mq_rq_state(req) != MQ_RQ_IN_FLIGHT)
@@ -506,6 +507,8 @@ bool nvme_cancel_request(struct request *req, void *data)
nvme_req(req)->status = NVME_SC_HOST_ABORTED_CMD;
nvme_req(req)->flags |= NVME_REQ_CANCELLED;
+ if ((nvme_req(rq)->flags & NVME_MPATH_CNT_ACTIVE))
+ atomic_dec(&ctrl->nr_active);
blk_mq_complete_request(req);
return true;
}
Please note that I am using atomic_dec() instead of atomic_dec_if_positive()
above for the same reason as Keith mentioned in his earlier mail.
> +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;
> + }
> + }
> +
> + 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 &&
> @@ -338,15 +384,27 @@ 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;
> @@ -798,6 +856,25 @@ static ssize_t nvme_subsys_iopolicy_show(struct device *dev,
> nvme_iopolicy_names[READ_ONCE(subsys->iopolicy)]);
> }
>
> +void nvme_subsys_iopolicy_update(struct nvme_subsystem *subsys, int iopolicy)
> +{
> + struct nvme_ctrl *ctrl;
> + int old_iopolicy = READ_ONCE(subsys->iopolicy);
> +
> + WRITE_ONCE(subsys->iopolicy, iopolicy);
> +
> + 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)
> {
> @@ -807,7 +884,7 @@ 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;
> }
> }
> @@ -905,6 +982,7 @@ void nvme_mpath_init_ctrl(struct nvme_ctrl *ctrl)
> mutex_init(&ctrl->ana_lock);
> timer_setup(&ctrl->anatt_timer, nvme_anatt_timeout, 0);
> INIT_WORK(&ctrl->ana_work, nvme_ana_work);
> + atomic_set(&ctrl->nr_active, 0);
> }
>
> int nvme_mpath_init_identify(struct nvme_ctrl *ctrl, struct nvme_id_ctrl *id)
> diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
> index f243a5822c2b..f5557889b244 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.
> @@ -190,6 +192,7 @@ 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)
> @@ -354,6 +357,7 @@ 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
> @@ -402,6 +406,7 @@ 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 {
> @@ -935,6 +940,7 @@ void nvme_mpath_clear_ctrl_paths(struct nvme_ctrl *ctrl);
> void nvme_mpath_shutdown_disk(struct nvme_ns_head *head);
> void nvme_mpath_start_request(struct request *rq);
> void nvme_mpath_end_request(struct request *rq);
> +void nvme_subsys_iopolicy_update(struct nvme_subsystem *subsys, int iopolicy);
>
> static inline void nvme_trace_bio_complete(struct request *req)
> {
> @@ -1034,6 +1040,9 @@ static inline bool nvme_disk_is_ns_head(struct gendisk *disk)
> {
> return false;
> }
> +static inline void nvme_subsys_iopolicy_update(struct nvme_subsystem *subsys, int iopolicy)
> +{
> +}
> #endif /* CONFIG_NVME_MULTIPATH */
>
> int nvme_ns_report_zones(struct nvme_ns *ns, sector_t sector,
Thanks,
--Nilay