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Message-ID: <20120830133820.GC21132@redhat.com>
Date: Thu, 30 Aug 2012 16:38:20 +0300
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Sasha Levin <levinsasha928@...il.com>
Cc: rusty@...tcorp.com.au, virtualization@...ts.linux-foundation.org,
linux-kernel@...r.kernel.org, avi@...hat.com, kvm@...r.kernel.org
Subject: Re: [PATCH v3 2/2] virtio-ring: Allocate indirect buffers from cache
when possible
On Thu, Aug 30, 2012 at 01:21:58PM +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@...il.com>
I am not sure we need these module params.
But assuming we keep them, we need to validate values - they come from
user.
> ---
> 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 | 34 ++++++++++++++++++++++++++++++----
> include/linux/virtio.h | 1 +
> net/9p/trans_virtio.c | 5 +++++
> 8 files changed, 56 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 7c63065..e4c6c42 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 3a644f1..ed22db8 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 da2e44c..8f30732 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 949c89e..a00e19d 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 = 16;
> module_param(indirect_thresh, uint, S_IRUGO);
>
> +static unsigned int indirect_alloc_thresh = 16;
Why 16? Please make is MAX_SG + 1 this makes some sense.
> +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 ca5ae7a..039c4a6 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 4063e03..dde867b 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;
>
> @@ -384,8 +391,14 @@ 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) {
> + u32 descs = vq->vring.desc[i].len / sizeof(struct vring_desc);
> + if (descs > vq->indirect_alloc_thresh)
> + kfree(phys_to_virt(vq->vring.desc[i].addr));
> + else
> + kmem_cache_free(vq->indirect_cache,
> + phys_to_virt(vq->vring.desc[i].addr));
> + }
If logic in two chunks above does not match it all
blows up. So let's add a helper is_cache(vq, buf)
and call from both places.
>
> while (vq->vring.desc[i].flags & VRING_DESC_F_NEXT) {
> i = vq->vring.desc[i].next;
> @@ -654,14 +667,25 @@ 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;
This means for virtio-net we still create a cache for both
TX and RX, but it's later unused for RX unless
big packet mode is set.
Pls make this flag per vq not per device.
> + if (vq->indirect_alloc_thresh) {
> + vq->indirect_cache =
> + KMEM_CACHE(vring_desc[vq->indirect_alloc_thresh], 0);
> +
> + if (vq->indirect_cache == NULL)
> + vq->indirect_alloc_thresh = 0;
> + }
> + }
>
> vq->event = virtio_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX);
>
> @@ -685,6 +709,8 @@ 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)
So what is a reasonable value?
It would be such that most bufs have # of s/g below it.
So I think 'expected_sg' would be a better name,
add documentation explaining what it is.
> diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
> index 418f933..058b6dd 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
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