From: Cong Wang Date: Wed, 6 Feb 2019 23:00:19 +0000 (-0800) Subject: mlx5: use RCU lock in mlx5_eq_cq_get() X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=1fbf1252df0e4212e17f98130cb5372b3bc019b0;p=linux.git mlx5: use RCU lock in mlx5_eq_cq_get() mlx5_eq_cq_get() is called in IRQ handler, the spinlock inside gets a lot of contentions when we test some heavy workload with 60 RX queues and 80 CPU's, and it is clearly shown in the flame graph. In fact, radix_tree_lookup() is perfectly fine with RCU read lock, we don't have to take a spinlock on this hot path. This is pretty much similar to commit 291c566a2891 ("net/mlx4_core: Fix racy CQ (Completion Queue) free"). Slow paths are still serialized with the spinlock, and with synchronize_irq() it should be safe to just move the fast path to RCU read lock. This patch itself reduces the latency by about 50% for our memcached workload on a 4.14 kernel we test. In upstream, as pointed out by Saeed, this spinlock gets some rework in commit 02d92f790364 ("net/mlx5: CQ Database per EQ"), so the difference could be smaller. Cc: Saeed Mahameed Cc: Tariq Toukan Acked-by: Saeed Mahameed Signed-off-by: Cong Wang Signed-off-by: Saeed Mahameed --- diff --git a/drivers/net/ethernet/mellanox/mlx5/core/eq.c b/drivers/net/ethernet/mellanox/mlx5/core/eq.c index ee04aab65a9f2..7092457705a24 100644 --- a/drivers/net/ethernet/mellanox/mlx5/core/eq.c +++ b/drivers/net/ethernet/mellanox/mlx5/core/eq.c @@ -114,11 +114,11 @@ static struct mlx5_core_cq *mlx5_eq_cq_get(struct mlx5_eq *eq, u32 cqn) struct mlx5_cq_table *table = &eq->cq_table; struct mlx5_core_cq *cq = NULL; - spin_lock(&table->lock); + rcu_read_lock(); cq = radix_tree_lookup(&table->tree, cqn); if (likely(cq)) mlx5_cq_hold(cq); - spin_unlock(&table->lock); + rcu_read_unlock(); return cq; } @@ -371,9 +371,9 @@ int mlx5_eq_add_cq(struct mlx5_eq *eq, struct mlx5_core_cq *cq) struct mlx5_cq_table *table = &eq->cq_table; int err; - spin_lock_irq(&table->lock); + spin_lock(&table->lock); err = radix_tree_insert(&table->tree, cq->cqn, cq); - spin_unlock_irq(&table->lock); + spin_unlock(&table->lock); return err; } @@ -383,9 +383,9 @@ int mlx5_eq_del_cq(struct mlx5_eq *eq, struct mlx5_core_cq *cq) struct mlx5_cq_table *table = &eq->cq_table; struct mlx5_core_cq *tmp; - spin_lock_irq(&table->lock); + spin_lock(&table->lock); tmp = radix_tree_delete(&table->tree, cq->cqn); - spin_unlock_irq(&table->lock); + spin_unlock(&table->lock); if (!tmp) { mlx5_core_warn(eq->dev, "cq 0x%x not found in eq 0x%x tree\n", eq->eqn, cq->cqn);