From 489beb91e66a237254e23ac1a0fe1beac23d87c5 Mon Sep 17 00:00:00 2001 From: Roland Dreier Date: Tue, 29 Aug 2017 10:33:44 -0700 Subject: [PATCH] nvme-fabrics: Convert nvmf_transports_mutex to an rwsem The mutex protects against the list of transports changing while a controller is being created, but using a plain old mutex means that it also serializes controller creation. This unnecessarily slows down creating multiple controllers - for example for the RDMA transport, creating a controller involves establishing one connection for every IO queue, which involves even more network/software round trips, so the delay can become significant. The simplest way to fix this is to change the mutex to an rwsem and only hold it for writing when the list is being mutated. Since we can take the rwsem for reading while creating a controller, we can create multiple controllers in parallel. Signed-off-by: Roland Dreier Reviewed-by: Sagi Grimberg Signed-off-by: Christoph Hellwig --- drivers/nvme/host/fabrics.c | 20 ++++++++++---------- 1 file changed, 10 insertions(+), 10 deletions(-) diff --git a/drivers/nvme/host/fabrics.c b/drivers/nvme/host/fabrics.c index fc3b6552f467..53a9598e3aee 100644 --- a/drivers/nvme/host/fabrics.c +++ b/drivers/nvme/host/fabrics.c @@ -22,7 +22,7 @@ #include "fabrics.h" static LIST_HEAD(nvmf_transports); -static DEFINE_MUTEX(nvmf_transports_mutex); +static DECLARE_RWSEM(nvmf_transports_rwsem); static LIST_HEAD(nvmf_hosts); static DEFINE_MUTEX(nvmf_hosts_mutex); @@ -495,9 +495,9 @@ int nvmf_register_transport(struct nvmf_transport_ops *ops) if (!ops->create_ctrl) return -EINVAL; - mutex_lock(&nvmf_transports_mutex); + down_write(&nvmf_transports_rwsem); list_add_tail(&ops->entry, &nvmf_transports); - mutex_unlock(&nvmf_transports_mutex); + up_write(&nvmf_transports_rwsem); return 0; } @@ -514,9 +514,9 @@ EXPORT_SYMBOL_GPL(nvmf_register_transport); */ void nvmf_unregister_transport(struct nvmf_transport_ops *ops) { - mutex_lock(&nvmf_transports_mutex); + down_write(&nvmf_transports_rwsem); list_del(&ops->entry); - mutex_unlock(&nvmf_transports_mutex); + up_write(&nvmf_transports_rwsem); } EXPORT_SYMBOL_GPL(nvmf_unregister_transport); @@ -525,7 +525,7 @@ static struct nvmf_transport_ops *nvmf_lookup_transport( { struct nvmf_transport_ops *ops; - lockdep_assert_held(&nvmf_transports_mutex); + lockdep_assert_held(&nvmf_transports_rwsem); list_for_each_entry(ops, &nvmf_transports, entry) { if (strcmp(ops->name, opts->transport) == 0) @@ -851,7 +851,7 @@ nvmf_create_ctrl(struct device *dev, const char *buf, size_t count) goto out_free_opts; opts->mask &= ~NVMF_REQUIRED_OPTS; - mutex_lock(&nvmf_transports_mutex); + down_read(&nvmf_transports_rwsem); ops = nvmf_lookup_transport(opts); if (!ops) { pr_info("no handler found for transport %s.\n", @@ -878,16 +878,16 @@ nvmf_create_ctrl(struct device *dev, const char *buf, size_t count) dev_warn(ctrl->device, "controller returned incorrect NQN: \"%s\".\n", ctrl->subnqn); - mutex_unlock(&nvmf_transports_mutex); + up_read(&nvmf_transports_rwsem); ctrl->ops->delete_ctrl(ctrl); return ERR_PTR(-EINVAL); } - mutex_unlock(&nvmf_transports_mutex); + up_read(&nvmf_transports_rwsem); return ctrl; out_unlock: - mutex_unlock(&nvmf_transports_mutex); + up_read(&nvmf_transports_rwsem); out_free_opts: nvmf_free_options(opts); return ERR_PTR(ret);