IB/mlx5: Postpone remove_keys under knowledge of coming preemption

The remove_keys() logic is performed as garbage collection task. Such
task is intended to be run when no other active processes are running.

The need_resched() will return TRUE if there are user tasks to be
activated in near future.

In such case, we don't execute remove_keys() and postpone
the garbage collection work to try to run in next cycle,
in order to free CPU resources to other tasks.

The possible pseudo-code to trigger such scenario:
1. Allocate a lot of MR to fill the cache above the limit.
2. Wait a small amount of time "to calm" the system.
3. Start CPU extensive operations on multi-node cluster.
4. Expect performance degradation during MR cache shrink operation.

Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Eli Cohen <eli@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

diff --git a/drivers/infiniband/hw/mlx5/mr.c b/drivers/infiniband/hw/mlx5/mr.c
index ec8993a7b3beea5a91370c1f66979dae583f49d4..6000f7aeede94301cbb7c281bfaae26299770106 100644 (file)
--- a/drivers/infiniband/hw/mlx5/mr.c
+++ b/drivers/infiniband/hw/mlx5/mr.c
@@ -381,7 +381,19 @@ static void __cache_work_func(struct mlx5_cache_ent *ent)
                        }
                }
        } else if (ent->cur > 2 * ent->limit) {
-               if (!someone_adding(cache) &&
+               /*
+                * The remove_keys() logic is performed as garbage collection
+                * task. Such task is intended to be run when no other active
+                * processes are running.
+                *
+                * The need_resched() will return TRUE if there are user tasks
+                * to be activated in near future.
+                *
+                * In such case, we don't execute remove_keys() and postpone
+                * the garbage collection work to try to run in next cycle,
+                * in order to free CPU resources to other tasks.
+                */
+               if (!need_resched() && !someone_adding(cache) &&
                    time_after(jiffies, cache->last_add + 300 * HZ)) {
                        remove_keys(dev, i, 1);
                        if (ent->cur > ent->limit)