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Message-ID: <CAJaqyWcxuyo3uN6Y9-LXjPtd+rJmeXi-BrDadAnuLhT3EyUieA@mail.gmail.com>
Date: Thu, 29 Aug 2024 19:12:46 +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 Thu, Aug 29, 2024 at 5:23 PM Dragos Tatulea <dtatulea@...dia.com> wrote:
>
>
>
> On 29.08.24 17:07, Eugenio Perez Martin wrote:
> > 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.
> >
> I want to believe it is :). I noticed during testing that this can
> interfere with the case where there are several .set_map() operations
> in quick succession. That's why the work is delayed by such a long
> time.
>
> It's not a perfect heuristic but I found that it's better than not
> having it.
>
Understood, thanks for explaining! Can you add the explanation to the macro?
It would be great to find a mechanism so the work is added in low
priority fashion, but I don't know any.
> >> + 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?
> >
> See above.
>
> >> + }
> >> }
> >>
> >> 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.
> Ack.
> >
> >> - mlx5_cmd_cleanup_async_ctx(&mvdev->async_ctx);
> >> }
> >>
> >> static const struct vdpa_mgmtdev_ops mdev_ops = {
> >> --
> >> 2.45.1
> >>
> >
>
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