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Date: Tue, 17 May 2022 16:59:00 -0700
From: Si-Wei Liu <si-wei.liu@...cle.com>
To: Eli Cohen <elic@...dia.com>, mst@...hat.com, jasowang@...hat.com
Cc: virtualization@...ts.linux-foundation.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 5/5] vdpa/mlx5: Use readers/writers semaphore instead
of mutex
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@...cle.com>
> Signed-off-by: Eli Cohen <elic@...dia.com>
Reviewed-by: Si-Wei Liu <si-wei.liu@...cle.com>
> ---
> 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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