Messages in this thread Patch in this message | | | From | Baegjae Sung <> | Subject | [PATCH] nvme-multipath: implement active-active round-robin path selector | Date | Tue, 27 Mar 2018 13:38:51 +0900 |
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Some storage environments (e.g., dual-port NVMe SSD) provide higher performance when using multiple paths simultaneously. Choosing a path from multiple paths in a round-robin fashion is a simple and efficient way to meet these requirements.
We implement the active-active round-robin path selector that chooses the path that is NVME_CTRL_LIVE and next to the previous path. By maintaining the structure of the active-standby path selector, we can easily switch between the active-standby path selector and the active-active round-robin path selector.
Example usage) # cat /sys/block/nvme0n1/mpath_policy [active-standby] round-robin # echo round-robin > /sys/block/nvme0n1/mpath_policy # cat /sys/block/nvme0n1/mpath_policy active-standby [round-robin]
Below are the results from a physical dual-port NVMe SSD using fio.
(MB/s) active-standby round-robin Random Read (4k) 1,672 2,640 Sequential Read (128k) 1,707 3,414 Random Write (4k) 1,450 1,728 Sequential Write (128k) 1,481 2,708
A single thread was used for sequential workloads and 16 threads were used for random workloads. The queue depth for each thread was 64.
Signed-off-by: Baegjae Sung <baegjae@gmail.com> --- drivers/nvme/host/core.c | 49 +++++++++++++++++++++++++++++++++++++++++++ drivers/nvme/host/multipath.c | 45 ++++++++++++++++++++++++++++++++++++++- drivers/nvme/host/nvme.h | 8 +++++++ 3 files changed, 101 insertions(+), 1 deletion(-)
diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c index 7aeca5db7916..cc91e8b247d0 100644 --- a/drivers/nvme/host/core.c +++ b/drivers/nvme/host/core.c @@ -68,6 +68,13 @@ static bool streams; module_param(streams, bool, 0644); MODULE_PARM_DESC(streams, "turn on support for Streams write directives"); +#ifdef CONFIG_NVME_MULTIPATH +static const char *const mpath_policy_name[] = { + [NVME_MPATH_ACTIVE_STANDBY] = "active-standby", + [NVME_MPATH_ROUND_ROBIN] = "round-robin", +}; +#endif + /* * nvme_wq - hosts nvme related works that are not reset or delete * nvme_reset_wq - hosts nvme reset works @@ -2603,12 +2610,51 @@ static ssize_t nsid_show(struct device *dev, struct device_attribute *attr, } static DEVICE_ATTR_RO(nsid); +#ifdef CONFIG_NVME_MULTIPATH +static ssize_t mpath_policy_show(struct device *dev, + struct device_attribute *attr, + char *buf) +{ + int i, len = 0; + struct nvme_ns_head *head = dev_to_ns_head(dev); + + for (i = 0;i < ARRAY_SIZE(mpath_policy_name);i++) { + if (i == head->mpath_policy) + len += sprintf(buf + len, "[%s] ", mpath_policy_name[i]); + else + len += sprintf(buf + len, "%s ", mpath_policy_name[i]); + } + len += sprintf(buf + len, "\n"); + return len; +} +static ssize_t mpath_policy_store(struct device *dev, + struct device_attribute *attr, const char *buf, + size_t count) +{ + int i; + struct nvme_ns_head *head = dev_to_ns_head(dev); + + for (i = 0;i < ARRAY_SIZE(mpath_policy_name);i++) { + if (strncmp(buf, mpath_policy_name[i], count - 1) == 0) { + head->mpath_policy = i; + dev_info(dev, "change mpath policy to %s\n", mpath_policy_name[i]); + } + } + return count; +} +static DEVICE_ATTR(mpath_policy, S_IRUGO | S_IWUSR, mpath_policy_show, \ + mpath_policy_store); +#endif + static struct attribute *nvme_ns_id_attrs[] = { &dev_attr_wwid.attr, &dev_attr_uuid.attr, &dev_attr_nguid.attr, &dev_attr_eui.attr, &dev_attr_nsid.attr, +#ifdef CONFIG_NVME_MULTIPATH + &dev_attr_mpath_policy.attr, +#endif NULL, }; @@ -2818,6 +2864,9 @@ static struct nvme_ns_head *nvme_alloc_ns_head(struct nvme_ctrl *ctrl, head->subsys = ctrl->subsys; head->ns_id = nsid; kref_init(&head->ref); +#ifdef CONFIG_NVME_MULTIPATH + head->mpath_policy = NVME_MPATH_ACTIVE_STANDBY; +#endif nvme_report_ns_ids(ctrl, nsid, id, &head->ids); diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c index 060f69e03427..6b6a15ccb542 100644 --- a/drivers/nvme/host/multipath.c +++ b/drivers/nvme/host/multipath.c @@ -75,6 +75,42 @@ inline struct nvme_ns *nvme_find_path(struct nvme_ns_head *head) return ns; } +inline struct nvme_ns *nvme_find_path_rr(struct nvme_ns_head *head) +{ + struct nvme_ns *prev_ns = srcu_dereference(head->current_path, &head->srcu); + struct nvme_ns *ns, *cand_ns = NULL; + bool after_prev_ns = false; + + /* + * Active-active round-robin path selector + * Choose the path that is NVME_CTRL_LIVE and next to the previous path + */ + + /* Case 1. If there is no previous path, choose the first LIVE path */ + if (!prev_ns) { + ns = __nvme_find_path(head); + return ns; + } + + list_for_each_entry_rcu(ns, &head->list, siblings) { + /* + * Case 2-1. Choose the first LIVE path from the next path of + * previous path to end + */ + if (after_prev_ns && ns->ctrl->state == NVME_CTRL_LIVE) { + rcu_assign_pointer(head->current_path, ns); + return ns; + } + /* Case 2-2. Mark the first LIVE path from start to previous path */ + if (!cand_ns && ns->ctrl->state == NVME_CTRL_LIVE) + cand_ns = ns; + if (ns == prev_ns) + after_prev_ns = true; + } + rcu_assign_pointer(head->current_path, cand_ns); + return cand_ns; +} + static blk_qc_t nvme_ns_head_make_request(struct request_queue *q, struct bio *bio) { @@ -85,7 +121,14 @@ static blk_qc_t nvme_ns_head_make_request(struct request_queue *q, int srcu_idx; srcu_idx = srcu_read_lock(&head->srcu); - ns = nvme_find_path(head); + switch (head->mpath_policy) { + case NVME_MPATH_ROUND_ROBIN: + ns = nvme_find_path_rr(head); + break; + case NVME_MPATH_ACTIVE_STANDBY: + default: + ns = nvme_find_path(head); + } if (likely(ns)) { bio->bi_disk = ns->disk; bio->bi_opf |= REQ_NVME_MPATH; diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h index d733b14ede9d..15e1163bbf2b 100644 --- a/drivers/nvme/host/nvme.h +++ b/drivers/nvme/host/nvme.h @@ -128,6 +128,13 @@ enum nvme_ctrl_state { NVME_CTRL_DEAD, }; +#ifdef CONFIG_NVME_MULTIPATH +enum nvme_mpath_policy { + NVME_MPATH_ACTIVE_STANDBY, + NVME_MPATH_ROUND_ROBIN, /* active-active round-robin */ +}; +#endif + struct nvme_ctrl { enum nvme_ctrl_state state; bool identified; @@ -250,6 +257,7 @@ struct nvme_ns_head { struct bio_list requeue_list; spinlock_t requeue_lock; struct work_struct requeue_work; + enum nvme_mpath_policy mpath_policy; #endif struct list_head list; struct srcu_struct srcu; -- 2.16.2
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