linux-kernel - [PATCH vhost v2 08/10] vdpa/mlx5: Keep notifiers during suspend but ignore

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Message-ID: <20240816090159.1967650-9-dtatulea@nvidia.com>
Date: Fri, 16 Aug 2024 12:01:57 +0300
From: Dragos Tatulea <dtatulea@...dia.com>
To: "Michael S . Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>,
	Eugenio Perez Martin <eperezma@...hat.com>,
	<virtualization@...ts.linux-foundation.org>
CC: Dragos Tatulea <dtatulea@...dia.com>, Si-Wei Liu <si-wei.liu@...cle.com>,
	Saeed Mahameed <saeedm@...dia.com>, Leon Romanovsky <leon@...nel.org>,
	<kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>, Gal Pressman
	<gal@...dia.com>, Parav Pandit <parav@...dia.com>, Xuan Zhuo
	<xuanzhuo@...ux.alibaba.com>, Tariq Toukan <tariqt@...dia.com>
Subject: [PATCH vhost v2 08/10] vdpa/mlx5: Keep notifiers during suspend but ignore

Unregistering notifiers is a costly operation. Instead of removing
the notifiers during device suspend and adding them back at resume,
simply ignore the call when the device is suspended.

At resume time call queue_link_work() to make sure that the device state
is propagated in case there were changes.

For 1 vDPA device x 32 VQs (16 VQPs) attached to a large VM (256 GB RAM,
32 CPUs x 2 threads per core), the device suspend time is reduced from
~13 ms to ~2.5 ms.

Signed-off-by: Dragos Tatulea <dtatulea@...dia.com>
Reviewed-by: Tariq Toukan <tariqt@...dia.com>
Acked-by: Eugenio Pérez <eperezma@...hat.com>
---
 drivers/vdpa/mlx5/net/mlx5_vnet.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
index 0773bec917be..65063c507130 100644
--- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
+++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
@@ -2850,6 +2850,9 @@ static int event_handler(struct notifier_block *nb, unsigned long event, void *p
 	struct mlx5_eqe *eqe = param;
 	int ret = NOTIFY_DONE;
 
+	if (ndev->mvdev.suspended)
+		return NOTIFY_DONE;
+
 	if (event == MLX5_EVENT_TYPE_PORT_CHANGE) {
 		switch (eqe->sub_type) {
 		case MLX5_PORT_CHANGE_SUBTYPE_DOWN:
@@ -3595,7 +3598,6 @@ static int mlx5_vdpa_suspend(struct vdpa_device *vdev)
 	mlx5_vdpa_info(mvdev, "suspending device\n");
 
 	down_write(&ndev->reslock);
-	unregister_link_notifier(ndev);
 	err = suspend_vqs(ndev, 0, ndev->cur_num_vqs);
 	mlx5_vdpa_cvq_suspend(mvdev);
 	mvdev->suspended = true;
@@ -3617,7 +3619,7 @@ static int mlx5_vdpa_resume(struct vdpa_device *vdev)
 	down_write(&ndev->reslock);
 	mvdev->suspended = false;
 	err = resume_vqs(ndev, 0, ndev->cur_num_vqs);
-	register_link_notifier(ndev);
+	queue_link_work(ndev);
 	up_write(&ndev->reslock);
 
 	return err;
-- 
2.45.1