Re: [PATCH v7 5/5] vdpa/mlx5: Use readers/writers semaphore instead of mutex

[Si-Wei Liu <si-wei.liu@xxxxxxxxxx>]

On 5/17/2022 6:13 AM, Eli Cohen wrote:
> Reading statistics could be done intensively and by several processes
> concurrently. Reader's lock is sufficient in this case.
>
> Change reslock from mutex to a rwsem.
>
> Suggested-by: Si-Wei Liu <si-wei.liu@xxxxxxxxxx>
> Signed-off-by: Eli Cohen <elic@xxxxxxxxxx>
Reviewed-by: Si-Wei Liu <si-wei.liu@xxxxxxxxxx>
> ---
>   drivers/vdpa/mlx5/net/mlx5_vnet.c | 41 ++++++++++++++-----------------
>   1 file changed, 19 insertions(+), 22 deletions(-)
>
> diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> index 2b815ef850c8..57cfc64248b7 100644
> --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
> +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> @@ -155,7 +155,7 @@ struct mlx5_vdpa_net {
>   	 * since memory map might change and we need to destroy and create
>   	 * resources while driver in operational.
>   	 */
> -	struct mutex reslock;
> +	struct rw_semaphore reslock;
>   	struct mlx5_flow_table *rxft;
>   	struct mlx5_fc *rx_counter;
>   	struct mlx5_flow_handle *rx_rule_ucast;
> @@ -1695,7 +1695,7 @@ static void mlx5_cvq_kick_handler(struct work_struct *work)
>   	ndev = to_mlx5_vdpa_ndev(mvdev);
>   	cvq = &mvdev->cvq;
>   
> -	mutex_lock(&ndev->reslock);
> +	down_write(&ndev->reslock);
>   
>   	if (!(mvdev->status & VIRTIO_CONFIG_S_DRIVER_OK))
>   		goto out;
> @@ -1746,7 +1746,7 @@ static void mlx5_cvq_kick_handler(struct work_struct *work)
>   	}
>   
>   out:
> -	mutex_unlock(&ndev->reslock);
> +	up_write(&ndev->reslock);
>   }
>   
>   static void mlx5_vdpa_kick_vq(struct vdpa_device *vdev, u16 idx)
> @@ -2244,7 +2244,7 @@ static int setup_driver(struct mlx5_vdpa_dev *mvdev)
>   	struct mlx5_vdpa_net *ndev = to_mlx5_vdpa_ndev(mvdev);
>   	int err;
>   
> -	WARN_ON(!mutex_is_locked(&ndev->reslock));
> +	WARN_ON(!rwsem_is_locked(&ndev->reslock));
>   
>   	if (ndev->setup) {
>   		mlx5_vdpa_warn(mvdev, "setup driver called for already setup driver\n");
> @@ -2292,7 +2292,7 @@ static int setup_driver(struct mlx5_vdpa_dev *mvdev)
>   static void teardown_driver(struct mlx5_vdpa_net *ndev)
>   {
>   
> -	WARN_ON(!mutex_is_locked(&ndev->reslock));
> +	WARN_ON(!rwsem_is_locked(&ndev->reslock));
>   
>   	if (!ndev->setup)
>   		return;
> @@ -2322,7 +2322,7 @@ static void mlx5_vdpa_set_status(struct vdpa_device *vdev, u8 status)
>   
>   	print_status(mvdev, status, true);
>   
> -	mutex_lock(&ndev->reslock);
> +	down_write(&ndev->reslock);
>   
>   	if ((status ^ ndev->mvdev.status) & VIRTIO_CONFIG_S_DRIVER_OK) {
>   		if (status & VIRTIO_CONFIG_S_DRIVER_OK) {
> @@ -2338,14 +2338,14 @@ static void mlx5_vdpa_set_status(struct vdpa_device *vdev, u8 status)
>   	}
>   
>   	ndev->mvdev.status = status;
> -	mutex_unlock(&ndev->reslock);
> +	up_write(&ndev->reslock);
>   	return;
>   
>   err_setup:
>   	mlx5_vdpa_destroy_mr(&ndev->mvdev);
>   	ndev->mvdev.status |= VIRTIO_CONFIG_S_FAILED;
>   err_clear:
> -	mutex_unlock(&ndev->reslock);
> +	up_write(&ndev->reslock);
>   }
>   
>   static int mlx5_vdpa_reset(struct vdpa_device *vdev)
> @@ -2356,7 +2356,7 @@ static int mlx5_vdpa_reset(struct vdpa_device *vdev)
>   	print_status(mvdev, 0, true);
>   	mlx5_vdpa_info(mvdev, "performing device reset\n");
>   
> -	mutex_lock(&ndev->reslock);
> +	down_write(&ndev->reslock);
>   	teardown_driver(ndev);
>   	clear_vqs_ready(ndev);
>   	mlx5_vdpa_destroy_mr(&ndev->mvdev);
> @@ -2371,7 +2371,7 @@ static int mlx5_vdpa_reset(struct vdpa_device *vdev)
>   		if (mlx5_vdpa_create_mr(mvdev, NULL))
>   			mlx5_vdpa_warn(mvdev, "create MR failed\n");
>   	}
> -	mutex_unlock(&ndev->reslock);
> +	up_write(&ndev->reslock);
>   
>   	return 0;
>   }
> @@ -2411,7 +2411,7 @@ static int mlx5_vdpa_set_map(struct vdpa_device *vdev, struct vhost_iotlb *iotlb
>   	bool change_map;
>   	int err;
>   
> -	mutex_lock(&ndev->reslock);
> +	down_write(&ndev->reslock);
>   
>   	err = mlx5_vdpa_handle_set_map(mvdev, iotlb, &change_map);
>   	if (err) {
> @@ -2423,7 +2423,7 @@ static int mlx5_vdpa_set_map(struct vdpa_device *vdev, struct vhost_iotlb *iotlb
>   		err = mlx5_vdpa_change_map(mvdev, iotlb);
>   
>   err:
> -	mutex_unlock(&ndev->reslock);
> +	up_write(&ndev->reslock);
>   	return err;
>   }
>   
> @@ -2442,7 +2442,6 @@ static void mlx5_vdpa_free(struct vdpa_device *vdev)
>   		mlx5_mpfs_del_mac(pfmdev, ndev->config.mac);
>   	}
>   	mlx5_vdpa_free_resources(&ndev->mvdev);
> -	mutex_destroy(&ndev->reslock);
>   	kfree(ndev->event_cbs);
>   	kfree(ndev->vqs);
>   }
> @@ -2527,7 +2526,7 @@ static int mlx5_vdpa_get_vendor_vq_stats(struct vdpa_device *vdev, u16 idx,
>   	u64 completed_desc;
>   	int err = 0;
>   
> -	mutex_lock(&ndev->reslock);
> +	down_read(&ndev->reslock);
>   	if (!is_index_valid(mvdev, idx)) {
>   		NL_SET_ERR_MSG_MOD(extack, "virtqueue index is not valid");
>   		err = -EINVAL;
> @@ -2566,7 +2565,7 @@ static int mlx5_vdpa_get_vendor_vq_stats(struct vdpa_device *vdev, u16 idx,
>   
>   	err = 0;
>   out_err:
> -	mutex_unlock(&ndev->reslock);
> +	up_read(&ndev->reslock);
>   	return err;
>   }
>   
> @@ -2835,18 +2834,18 @@ static int mlx5_vdpa_dev_add(struct vdpa_mgmt_dev *v_mdev, const char *name,
>   	}
>   
>   	init_mvqs(ndev);
> -	mutex_init(&ndev->reslock);
> +	init_rwsem(&ndev->reslock);
>   	config = &ndev->config;
>   
>   	if (add_config->mask & BIT_ULL(VDPA_ATTR_DEV_NET_CFG_MTU)) {
>   		err = config_func_mtu(mdev, add_config->net.mtu);
>   		if (err)
> -			goto err_mtu;
> +			goto err_alloc;
>   	}
>   
>   	err = query_mtu(mdev, &mtu);
>   	if (err)
> -		goto err_mtu;
> +		goto err_alloc;
>   
>   	ndev->config.mtu = cpu_to_mlx5vdpa16(mvdev, mtu);
>   
> @@ -2860,14 +2859,14 @@ static int mlx5_vdpa_dev_add(struct vdpa_mgmt_dev *v_mdev, const char *name,
>   	} else {
>   		err = mlx5_query_nic_vport_mac_address(mdev, 0, 0, config->mac);
>   		if (err)
> -			goto err_mtu;
> +			goto err_alloc;
>   	}
>   
>   	if (!is_zero_ether_addr(config->mac)) {
>   		pfmdev = pci_get_drvdata(pci_physfn(mdev->pdev));
>   		err = mlx5_mpfs_add_mac(pfmdev, config->mac);
>   		if (err)
> -			goto err_mtu;
> +			goto err_alloc;
>   
>   		ndev->mvdev.mlx_features |= BIT_ULL(VIRTIO_NET_F_MAC);
>   	}
> @@ -2917,8 +2916,6 @@ static int mlx5_vdpa_dev_add(struct vdpa_mgmt_dev *v_mdev, const char *name,
>   err_mpfs:
>   	if (!is_zero_ether_addr(config->mac))
>   		mlx5_mpfs_del_mac(pfmdev, config->mac);
> -err_mtu:
> -	mutex_destroy(&ndev->reslock);
>   err_alloc:
>   	put_device(&mvdev->vdev.dev);
>   	return err;

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