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Message-ID: <CAJaqyWfANjzrKk9J=hJrdv6c8xd5Xx81XyigPBvc--AxQQK_gg@mail.gmail.com>
Date: Thu, 29 Aug 2024 17:07:54 +0200
From: Eugenio Perez Martin <eperezma@...hat.com>
To: Dragos Tatulea <dtatulea@...dia.com>
Cc: "Michael S . Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>,
Si-Wei Liu <si-wei.liu@...cle.com>, virtualization@...ts.linux-foundation.org,
Gal Pressman <gal@...dia.com>, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
Parav Pandit <parav@...dia.com>, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
Cosmin Ratiu <cratiu@...dia.com>
Subject: Re: [PATCH vhost 7/7] vdpa/mlx5: Postpone MR deletion
On Wed, Aug 21, 2024 at 1:42 PM Dragos Tatulea <dtatulea@...dia.com> wrote:
>
> Currently, when a new MR is set up, the old MR is deleted. MR deletion
> is about 30-40% the time of MR creation. As deleting the old MR is not
> important for the process of setting up the new MR, this operation
> can be postponed.
>
> This series adds a workqueue that does MR garbage collection at a later
> point. If the MR lock is taken, the handler will back off and
> reschedule. The exception during shutdown: then the handler must
> not postpone the work.
>
> Note that this is only a speculative optimization: if there is some
> mapping operation that is triggered while the garbage collector handler
> has the lock taken, this operation it will have to wait for the handler
> to finish.
>
> Signed-off-by: Dragos Tatulea <dtatulea@...dia.com>
> Reviewed-by: Cosmin Ratiu <cratiu@...dia.com>
> ---
> drivers/vdpa/mlx5/core/mlx5_vdpa.h | 10 ++++++
> drivers/vdpa/mlx5/core/mr.c | 51 ++++++++++++++++++++++++++++--
> drivers/vdpa/mlx5/net/mlx5_vnet.c | 3 +-
> 3 files changed, 60 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/vdpa/mlx5/core/mlx5_vdpa.h b/drivers/vdpa/mlx5/core/mlx5_vdpa.h
> index c3e17bc888e8..2cedf7e2dbc4 100644
> --- a/drivers/vdpa/mlx5/core/mlx5_vdpa.h
> +++ b/drivers/vdpa/mlx5/core/mlx5_vdpa.h
> @@ -86,8 +86,18 @@ enum {
> struct mlx5_vdpa_mr_resources {
> struct mlx5_vdpa_mr *mr[MLX5_VDPA_NUM_AS];
> unsigned int group2asid[MLX5_VDPA_NUMVQ_GROUPS];
> +
> + /* Pre-deletion mr list */
> struct list_head mr_list_head;
> +
> + /* Deferred mr list */
> + struct list_head mr_gc_list_head;
> + struct workqueue_struct *wq_gc;
> + struct delayed_work gc_dwork_ent;
> +
> struct mutex lock;
> +
> + atomic_t shutdown;
> };
>
> struct mlx5_vdpa_dev {
> diff --git a/drivers/vdpa/mlx5/core/mr.c b/drivers/vdpa/mlx5/core/mr.c
> index ec75f165f832..43fce6b39cf2 100644
> --- a/drivers/vdpa/mlx5/core/mr.c
> +++ b/drivers/vdpa/mlx5/core/mr.c
> @@ -653,14 +653,46 @@ static void _mlx5_vdpa_destroy_mr(struct mlx5_vdpa_dev *mvdev, struct mlx5_vdpa_
> kfree(mr);
> }
>
> +#define MLX5_VDPA_MR_GC_TRIGGER_MS 2000
> +
> +static void mlx5_vdpa_mr_gc_handler(struct work_struct *work)
> +{
> + struct mlx5_vdpa_mr_resources *mres;
> + struct mlx5_vdpa_mr *mr, *tmp;
> + struct mlx5_vdpa_dev *mvdev;
> +
> + mres = container_of(work, struct mlx5_vdpa_mr_resources, gc_dwork_ent.work);
> +
> + if (atomic_read(&mres->shutdown)) {
> + mutex_lock(&mres->lock);
> + } else if (!mutex_trylock(&mres->lock)) {
Is the trylock worth it? My understanding is that mutex_lock will add
the kthread to the waitqueue anyway if it is not able to acquire the
lock.
> + queue_delayed_work(mres->wq_gc, &mres->gc_dwork_ent,
> + msecs_to_jiffies(MLX5_VDPA_MR_GC_TRIGGER_MS));
> + return;
> + }
> +
> + mvdev = container_of(mres, struct mlx5_vdpa_dev, mres);
> +
> + list_for_each_entry_safe(mr, tmp, &mres->mr_gc_list_head, mr_list) {
> + _mlx5_vdpa_destroy_mr(mvdev, mr);
> + }
> +
> + mutex_unlock(&mres->lock);
> +}
> +
> static void _mlx5_vdpa_put_mr(struct mlx5_vdpa_dev *mvdev,
> struct mlx5_vdpa_mr *mr)
> {
> + struct mlx5_vdpa_mr_resources *mres = &mvdev->mres;
> +
> if (!mr)
> return;
>
> - if (refcount_dec_and_test(&mr->refcount))
> - _mlx5_vdpa_destroy_mr(mvdev, mr);
> + if (refcount_dec_and_test(&mr->refcount)) {
> + list_move_tail(&mr->mr_list, &mres->mr_gc_list_head);
> + queue_delayed_work(mres->wq_gc, &mres->gc_dwork_ent,
> + msecs_to_jiffies(MLX5_VDPA_MR_GC_TRIGGER_MS));
Why the delay?
> + }
> }
>
> void mlx5_vdpa_put_mr(struct mlx5_vdpa_dev *mvdev,
> @@ -848,9 +880,17 @@ int mlx5_vdpa_init_mr_resources(struct mlx5_vdpa_dev *mvdev)
> {
> struct mlx5_vdpa_mr_resources *mres = &mvdev->mres;
>
> - INIT_LIST_HEAD(&mres->mr_list_head);
> + mres->wq_gc = create_singlethread_workqueue("mlx5_vdpa_mr_gc");
> + if (!mres->wq_gc)
> + return -ENOMEM;
> +
> + INIT_DELAYED_WORK(&mres->gc_dwork_ent, mlx5_vdpa_mr_gc_handler);
> +
> mutex_init(&mres->lock);
>
> + INIT_LIST_HEAD(&mres->mr_list_head);
> + INIT_LIST_HEAD(&mres->mr_gc_list_head);
> +
> return 0;
> }
>
> @@ -858,5 +898,10 @@ void mlx5_vdpa_destroy_mr_resources(struct mlx5_vdpa_dev *mvdev)
> {
> struct mlx5_vdpa_mr_resources *mres = &mvdev->mres;
>
> + atomic_set(&mres->shutdown, 1);
> +
> + flush_delayed_work(&mres->gc_dwork_ent);
> + destroy_workqueue(mres->wq_gc);
> + mres->wq_gc = NULL;
> mutex_destroy(&mres->lock);
> }
> diff --git a/drivers/vdpa/mlx5/net/mlx5_vnet.c b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> index 1cadcb05a5c7..ee9482ef51e6 100644
> --- a/drivers/vdpa/mlx5/net/mlx5_vnet.c
> +++ b/drivers/vdpa/mlx5/net/mlx5_vnet.c
> @@ -3435,6 +3435,8 @@ static void mlx5_vdpa_free(struct vdpa_device *vdev)
> free_fixed_resources(ndev);
> mlx5_vdpa_clean_mrs(mvdev);
> mlx5_vdpa_destroy_mr_resources(&ndev->mvdev);
> + mlx5_cmd_cleanup_async_ctx(&mvdev->async_ctx);
> +
> if (!is_zero_ether_addr(ndev->config.mac)) {
> pfmdev = pci_get_drvdata(pci_physfn(mvdev->mdev->pdev));
> mlx5_mpfs_del_mac(pfmdev, ndev->config.mac);
> @@ -4044,7 +4046,6 @@ static void mlx5_vdpa_dev_del(struct vdpa_mgmt_dev *v_mdev, struct vdpa_device *
> destroy_workqueue(wq);
> mgtdev->ndev = NULL;
>
Extra newline here.
> - mlx5_cmd_cleanup_async_ctx(&mvdev->async_ctx);
> }
>
> static const struct vdpa_mgmtdev_ops mdev_ops = {
> --
> 2.45.1
>
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