Re: [PATCH v2 2/2] virtio-ring: Allocate indirect buffers from cache when possible

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Aug 28, 2012 at 03:04:03PM +0200, Sasha Levin wrote:
> Currently if VIRTIO_RING_F_INDIRECT_DESC is enabled we will
> use indirect descriptors and allocate them using a simple
> kmalloc().
> 
> This patch adds a cache which will allow indirect buffers under
> a configurable size to be allocated from that cache instead.
> 
> Signed-off-by: Sasha Levin <levinsasha928@gmail.com>

The API is ugly - how does driver know what to set?
Is this a typical request size? Then let's call it that.

Also this is really per VQ, right?

What is a good default for net? I guess max sg?

> ---
> 
> Changes in v2:
> 
>  - Free correctly indirect buffers.
> 
>  drivers/block/virtio_blk.c          |  4 ++++
>  drivers/char/hw_random/virtio-rng.c |  4 ++++
>  drivers/char/virtio_console.c       |  4 ++++
>  drivers/net/virtio_net.c            |  4 ++++
>  drivers/virtio/virtio_balloon.c     |  4 ++++
>  drivers/virtio/virtio_ring.c        | 28 ++++++++++++++++++++++++----
>  include/linux/virtio.h              |  1 +
>  net/9p/trans_virtio.c               |  5 +++++
>  8 files changed, 50 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 13b8ae9..7f670af 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -25,6 +25,9 @@ struct workqueue_struct *virtblk_wq;
>  static unsigned int indirect_thresh;
>  module_param(indirect_thresh, uint, S_IRUGO);
>  
> +static unsigned int indirect_alloc_thresh;
> +module_param(indirect_alloc_thresh, uint, S_IRUGO);
> +
>  struct virtio_blk
>  {
>  	struct virtio_device *vdev;
> @@ -739,6 +742,7 @@ static int __devinit virtblk_probe(struct virtio_device *vdev)
>  	INIT_WORK(&vblk->config_work, virtblk_config_changed_work);
>  	vblk->config_enable = true;
>  	vdev->indirect_thresh = indirect_thresh;
> +	vdev->indirect_alloc_thresh = indirect_alloc_thresh;
>  
>  	err = init_vq(vblk);
>  	if (err)
> diff --git a/drivers/char/hw_random/virtio-rng.c b/drivers/char/hw_random/virtio-rng.c
> index 02d8421..8475ece 100644
> --- a/drivers/char/hw_random/virtio-rng.c
> +++ b/drivers/char/hw_random/virtio-rng.c
> @@ -28,6 +28,9 @@
>  static unsigned int indirect_thresh;
>  module_param(indirect_thresh, uint, S_IRUGO);
>  
> +static unsigned int indirect_alloc_thresh;
> +module_param(indirect_alloc_thresh, uint, S_IRUGO);
> +
>  static struct virtqueue *vq;
>  static unsigned int data_avail;
>  static DECLARE_COMPLETION(have_data);
> @@ -97,6 +100,7 @@ static int probe_common(struct virtio_device *vdev)
>  
>  	/* We expect a single virtqueue. */
>  	vdev->indirect_thresh = indirect_thresh;
> +	vdev->indirect_alloc_thresh = indirect_alloc_thresh;
>  	vq = virtio_find_single_vq(vdev, random_recv_done, "input");
>  	if (IS_ERR(vq))
>  		return PTR_ERR(vq);
> diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
> index fc14e7f..c6f24a7 100644
> --- a/drivers/char/virtio_console.c
> +++ b/drivers/char/virtio_console.c
> @@ -42,6 +42,9 @@
>  static unsigned int indirect_thresh;
>  module_param(indirect_thresh, uint, S_IRUGO);
>  
> +static unsigned int indirect_alloc_thresh;
> +module_param(indirect_alloc_thresh, uint, S_IRUGO);
> +
>  /*
>   * This is a global struct for storing common data for all the devices
>   * this driver handles.
> @@ -1891,6 +1894,7 @@ static int __devinit virtcons_probe(struct virtio_device *vdev)
>  			      &portdev->config.max_nr_ports) == 0)
>  		multiport = true;
>  	vdev->indirect_thresh = indirect_thresh;
> +	vdev->indirect_alloc_thresh = indirect_alloc_thresh;
>  
>  	err = init_vqs(portdev);
>  	if (err < 0) {
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 64a8321..c091efd 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -37,6 +37,9 @@ module_param(gso, bool, 0444);
>  static unsigned int indirect_thresh;
>  module_param(indirect_thresh, uint, S_IRUGO);
>  
> +static unsigned int indirect_alloc_thresh;
> +module_param(indirect_alloc_thresh, uint, S_IRUGO);
> +
>  /* FIXME: MTU in config. */
>  #define MAX_PACKET_LEN (ETH_HLEN + VLAN_HLEN + ETH_DATA_LEN)
>  #define GOOD_COPY_LEN	128
> @@ -1132,6 +1135,7 @@ static int virtnet_probe(struct virtio_device *vdev)
>  	if (virtio_has_feature(vdev, VIRTIO_NET_F_MRG_RXBUF))
>  		vi->mergeable_rx_bufs = true;
>  	vdev->indirect_thresh = indirect_thresh;
> +	vdev->indirect_alloc_thresh = indirect_alloc_thresh;
>  
>  	err = init_vqs(vi);
>  	if (err)
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index fce7347..ccf87db 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -38,6 +38,9 @@
>  static unsigned int indirect_thresh;
>  module_param(indirect_thresh, uint, S_IRUGO);
>  
> +static unsigned int indirect_alloc_thresh;
> +module_param(indirect_alloc_thresh, uint, S_IRUGO);
> +
>  struct virtio_balloon
>  {
>  	struct virtio_device *vdev;
> @@ -360,6 +363,7 @@ static int virtballoon_probe(struct virtio_device *vdev)
>  	vb->vdev = vdev;
>  	vb->need_stats_update = 0;
>  	vdev->indirect_thresh = indirect_thresh;
> +	vdev->indirect_alloc_thresh = indirect_alloc_thresh;
>  
>  	err = init_vqs(vb);
>  	if (err)
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 99a64a7..e8b9c54 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -93,6 +93,10 @@ struct vring_virtqueue
>  	 */
>  	unsigned int indirect_thresh;
>  
> +	/* Buffers below this size will be allocated from cache */
> +	unsigned int indirect_alloc_thresh;
> +	struct kmem_cache *indirect_cache;
> +
>  	/* Host publishes avail event idx */
>  	bool event;
>  
> @@ -135,7 +139,10 @@ static int vring_add_indirect(struct vring_virtqueue *vq,
>  	unsigned head;
>  	int i;
>  
> -	desc = kmalloc((out + in) * sizeof(struct vring_desc), gfp);
> +	if ((out + in) <= vq->indirect_alloc_thresh)
> +		desc = kmem_cache_alloc(vq->indirect_cache, gfp);
> +	else
> +		desc = kmalloc((out + in) * sizeof(struct vring_desc), gfp);
>  	if (!desc)
>  		return -ENOMEM;

So this means that drivers need to know how large each
descriptor is to avoid trying to allocate 32Mbyte chunks :)

>  
> @@ -384,8 +391,13 @@ static void detach_buf(struct vring_virtqueue *vq, unsigned int head)
>  	i = head;
>  
>  	/* Free the indirect table */
> -	if (vq->vring.desc[i].flags & VRING_DESC_F_INDIRECT)
> -		kfree(phys_to_virt(vq->vring.desc[i].addr));
> +	if (vq->vring.desc[i].flags & VRING_DESC_F_INDIRECT) {
> +		if (vq->vring.desc[i].len > vq->indirect_alloc_thresh)

This looks wrong. indirect_alloc_thresh is in entries but len is in
bytes, isn't it?


> +			kfree(phys_to_virt(vq->vring.desc[i].addr));
> +		else
> +			kmem_cache_free(vq->indirect_cache,
> +					phys_to_virt(vq->vring.desc[i].addr));
> +	}
>  
>  	while (vq->vring.desc[i].flags & VRING_DESC_F_NEXT) {
>  		i = vq->vring.desc[i].next;
> @@ -654,14 +666,20 @@ struct virtqueue *vring_new_virtqueue(unsigned int num,
>  	vq->last_used_idx = 0;
>  	vq->num_added = 0;
>  	vq->indirect_thresh = 0;
> +	vq->indirect_alloc_thresh = 0;
> +	vq->indirect_cache = NULL;
>  	list_add_tail(&vq->vq.list, &vdev->vqs);
>  #ifdef DEBUG
>  	vq->in_use = false;
>  	vq->last_add_time_valid = false;
>  #endif
>  
> -	if (virtio_has_feature(vdev, VIRTIO_RING_F_INDIRECT_DESC))
> +	if (virtio_has_feature(vdev, VIRTIO_RING_F_INDIRECT_DESC)) {
>  		vq->indirect_thresh = vdev->indirect_thresh;
> +		vq->indirect_alloc_thresh = vdev->indirect_alloc_thresh;
> +		if (vq->indirect_alloc_thresh)
> +			vq->indirect_cache = KMEM_CACHE(vring_desc[vq->indirect_alloc_thresh],
> 0);

I am not a purist but this line looks way too long.
Also - no need to check cache creation succeeded?
On failure - disable caching?

Also - let's check that values are sane before passing them on?
They come from user after all.

Also - should not threshold be per VQ? E.g. for -net we do not
need the cache for RX unless in legacy big packet mode.

> +	}
>  
>  	vq->event = virtio_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX);
>  
> @@ -685,6 +703,8 @@ EXPORT_SYMBOL_GPL(vring_new_virtqueue);
>  void vring_del_virtqueue(struct virtqueue *vq)
>  {
>  	list_del(&vq->list);
> +	if (to_vvq(vq)->indirect_cache)
> +		kmem_cache_destroy(to_vvq(vq)->indirect_cache);
>  	kfree(to_vvq(vq));
>  }
>  EXPORT_SYMBOL_GPL(vring_del_virtqueue);
> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> index 48bc457..3261c02 100644
> --- a/include/linux/virtio.h
> +++ b/include/linux/virtio.h
> @@ -70,6 +70,7 @@ struct virtio_device {
>  	unsigned long features[1];
>  	void *priv;
>  	unsigned int indirect_thresh;
> +	unsigned int indirect_alloc_thresh;
>  };
>  
>  #define dev_to_virtio(dev) container_of(dev, struct virtio_device, dev)
> diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
> index fc93962..3044c86 100644
> --- a/net/9p/trans_virtio.c
> +++ b/net/9p/trans_virtio.c
> @@ -55,6 +55,9 @@
>  static unsigned int indirect_thresh;
>  module_param(indirect_thresh, uint, S_IRUGO);
>  
> +static unsigned int indirect_alloc_thresh;
> +module_param(indirect_alloc_thresh, uint, S_IRUGO);
> +
>  /* a single mutex to manage channel initialization and attachment */
>  static DEFINE_MUTEX(virtio_9p_lock);
>  static DECLARE_WAIT_QUEUE_HEAD(vp_wq);
> @@ -505,6 +508,8 @@ static int p9_virtio_probe(struct virtio_device *vdev)
>  
>  	/* We expect one virtqueue, for requests. */
>  	vdev->indirect_thresh = indirect_thresh;
> +	vdev->indirect_alloc_thresh = indirect_alloc_thresh;
> +
>  	chan->vq = virtio_find_single_vq(vdev, req_done, "requests");
>  	if (IS_ERR(chan->vq)) {
>  		err = PTR_ERR(chan->vq);
> -- 
> 1.7.12