[Linaro-mm-sig] Re: [PATCH net-next 1/4] net: devmem: allow rx-buf-size > PAGE_SIZE per dmabuf binding

On 06/03, Bobby Eshleman wrote:

From: Bobby Eshleman bobbyeshleman@meta.com

Every devmem dmabuf binding today hands the page_pool PAGE_SIZE niovs. This caps a single RX descriptor at PAGE_SIZE, burning CPU on buffer churn for large flows.

Add a bind-time netlink attribute, NETDEV_A_DMABUF_RX_BUF_SIZE, that lets userspace request a larger niov size. The value must be a power of two >= PAGE_SIZE.

Measurements

Setup: kperf in devmem RX/TX cuda mode, 4 flows, 64 MB messages, 60s, dctcp, num-rx-queues=4, dmabuf-rx/tx-size-mb=2048, 10 runs per niov size, mlx5.

CPU Util:

niov net sirq % net idle % app sys % app idle %

---

 4K   62.38 +/-  8.27   33.40 +/-  7.51   54.15 +/- 10.23   43.67 +/- 10.53
16K   58.91 +/-  5.35   35.23 +/-  5.88   41.05 +/-  8.87   56.42 +/-  9.24
32K   64.12 +/-  0.68   31.09 +/-  1.48   44.54 +/-  3.51   52.63 +/-  3.65
64K   54.69 +/-  5.54   39.67 +/-  5.81   35.47 +/-  3.11   61.97 +/-  3.27

RX app sys % drops ~19% from 4K to 64K.

Throughput:

niov RX dev Gbps RX flow avg Gbps

---

 4K  300.63 +/- 53.21    75.16 +/- 13.30
16K  321.35 +/- 28.20    80.34 +/-  7.05
32K  347.63 +/-  2.20    86.91 +/-  0.55
64K  332.11 +/- 14.26    83.03 +/-  3.56

Throughput seems to increase, but the stdev is pretty wide so could just be noise.

kperf support (not yet merged): https://github.com/facebookexperimental/kperf/commit/8837577f920876bce6986ec...

Signed-off-by: Bobby Eshleman bobbyeshleman@meta.com

Documentation/netlink/specs/netdev.yaml | 8 +++++ include/uapi/linux/netdev.h | 1 + net/core/devmem.c | 52 +++++++++++++++++++-------------- net/core/devmem.h | 13 ++++++--- net/core/netdev-genl-gen.c | 5 ++-- net/core/netdev-genl.c | 18 ++++++++++-- tools/include/uapi/linux/netdev.h | 1 + 7 files changed, 68 insertions(+), 30 deletions(-)

diff --git a/Documentation/netlink/specs/netdev.yaml b/Documentation/netlink/specs/netdev.yaml index a1f4c5a561e9..063119907983 100644 --- a/Documentation/netlink/specs/netdev.yaml +++ b/Documentation/netlink/specs/netdev.yaml @@ -591,6 +591,13 @@ attribute-sets: type: u32 checks: min: 1

•  -
  

•    name: rx-buf-size
  

•    doc: |
  

•      Size in bytes of each RX buffer the NIC writes into from the bound
  

•      dmabuf. Must be a power of two and >= PAGE_SIZE; defaults to
  

•      PAGE_SIZE.
  

•    type: u32
  

operations: list: @@ -805,6 +812,7 @@ operations: - ifindex - fd - queues

•        - rx-buf-size
     reply:
       attributes:
         - id
  

diff --git a/include/uapi/linux/netdev.h b/include/uapi/linux/netdev.h index 7df1056a35fd..180a4ffffd60 100644 --- a/include/uapi/linux/netdev.h +++ b/include/uapi/linux/netdev.h @@ -217,6 +217,7 @@ enum { NETDEV_A_DMABUF_QUEUES, NETDEV_A_DMABUF_FD, NETDEV_A_DMABUF_ID,

• NETDEV_A_DMABUF_RX_BUF_SIZE,

__NETDEV_A_DMABUF_MAX, NETDEV_A_DMABUF_MAX = (__NETDEV_A_DMABUF_MAX - 1) diff --git a/net/core/devmem.c b/net/core/devmem.c index 957d6b96216b..5a1c0d7984a8 100644 --- a/net/core/devmem.c +++ b/net/core/devmem.c @@ -46,7 +46,7 @@ static dma_addr_t net_devmem_get_dma_addr(const struct net_iov *niov) owner = net_devmem_iov_to_chunk_owner(niov); return owner->base_dma_addr +

•       ((dma_addr_t)net_iov_idx(niov) << PAGE_SHIFT);
  

•       ((dma_addr_t)net_iov_idx(niov) << owner->binding->niov_shift);
  

} static void net_devmem_dmabuf_binding_release(struct percpu_ref *ref) @@ -93,13 +93,14 @@ net_devmem_alloc_dmabuf(struct net_devmem_dmabuf_binding *binding) ssize_t offset; ssize_t index;

• dma_addr = gen_pool_alloc_owner(binding->chunk_pool, PAGE_SIZE,

• dma_addr = gen_pool_alloc_owner(binding->chunk_pool,

• 			1UL << binding->niov_shift,
  		(void **)&owner);
  

  if (!dma_addr) return NULL;

offset = dma_addr - owner->base_dma_addr;

• index = offset / PAGE_SIZE;

• index = offset >> binding->niov_shift; niov = &owner->area.niovs[index];

niov->desc.pp_magic = 0; @@ -113,12 +114,13 @@ void net_devmem_free_dmabuf(struct net_iov *niov) { struct net_devmem_dmabuf_binding *binding = net_devmem_iov_binding(niov); unsigned long dma_addr = net_devmem_get_dma_addr(niov);

• size_t niov_size = 1UL << binding->niov_shift;

if (WARN_ON(!gen_pool_has_addr(binding->chunk_pool, dma_addr,

• 		       PAGE_SIZE)))
  

• 		       niov_size)))
  

  return;

• gen_pool_free(binding->chunk_pool, dma_addr, PAGE_SIZE);

• gen_pool_free(binding->chunk_pool, dma_addr, niov_size);

} void net_devmem_unbind_dmabuf(struct net_devmem_dmabuf_binding *binding) @@ -163,6 +165,9 @@ int net_devmem_bind_dmabuf_to_queue(struct net_device *dev, u32 rxq_idx, u32 xa_idx; int err;

• if (binding->niov_shift != PAGE_SHIFT)

• mp_params.rx_page_size = 1U << binding->niov_shift;
  

• err = netif_mp_open_rxq(dev, rxq_idx, &mp_params, extack); if (err) return err;

@@ -184,14 +189,16 @@ struct net_devmem_dmabuf_binding * net_devmem_bind_dmabuf(struct net_device *dev, void *vdev, struct device *dma_dev, enum dma_data_direction direction,

•        unsigned int dmabuf_fd, struct netdev_nl_sock *priv,
  

•        unsigned int dmabuf_fd, unsigned int niov_shift,
  

•        struct netdev_nl_sock *priv,
    struct netlink_ext_ack *extack)
  

{ struct net_devmem_dmabuf_binding *binding;

• size_t niov_size = 1UL << niov_shift; static u32 id_alloc_next;
• unsigned int sg_idx, i; struct scatterlist *sg; struct dma_buf *dmabuf;

• unsigned int sg_idx, i; unsigned long virtual; int err;

@@ -213,6 +220,7 @@ net_devmem_bind_dmabuf(struct net_device *dev, void *vdev, binding->dev = dev; binding->vdev = vdev;

• binding->niov_shift = niov_shift; xa_init_flags(&binding->bound_rxqs, XA_FLAGS_ALLOC);

err = percpu_ref_init(&binding->ref, @@ -248,18 +256,14 @@ net_devmem_bind_dmabuf(struct net_device *dev, void *vdev, goto err_unmap; } binding->tx_vec = kvmalloc_objs(struct net_iov *,

• 				dmabuf->size / PAGE_SIZE);
  

• 				dmabuf->size >> niov_shift);
  

  if (!binding->tx_vec) { err = -ENOMEM; goto err_unmap; } }

• /* For simplicity we expect to make PAGE_SIZE allocations, but the

• * binding can be much more flexible than that. We may be able to
  

• * allocate MTU sized chunks here. Leave that for future work...
  

• */
  

• binding->chunk_pool = gen_pool_create(PAGE_SHIFT,

• binding->chunk_pool = gen_pool_create(niov_shift, dev_to_node(&dev->dev)); if (!binding->chunk_pool) { err = -ENOMEM;

@@ -273,9 +277,11 @@ net_devmem_bind_dmabuf(struct net_device *dev, void *vdev, size_t len = sg_dma_len(sg); struct net_iov *niov;

• if (!IS_ALIGNED(len, PAGE_SIZE)) {
  

• if (!IS_ALIGNED(dma_addr, niov_size) ||
  

•     !IS_ALIGNED(len, niov_size)) {
  err = -EINVAL;
  

• 	NL_SET_ERR_MSG(extack, "dma-buf SG length must be PAGE_SIZE aligned");
  

• 	NL_SET_ERR_MSG(extack,
  

• 		       "dmabuf sg entry not aligned to niov size");
  

nit: should we NL_SET_ERR_MSG_FMT here and export chunk len and expected alignment?

	goto err_free_chunks;
}

@@ -288,7 +294,7 @@ net_devmem_bind_dmabuf(struct net_device *dev, void *vdev, owner->area.base_virtual = virtual; owner->base_dma_addr = dma_addr;

• owner->area.num_niovs = len / PAGE_SIZE;
  

• owner->area.num_niovs = len >> niov_shift;
  

  owner->binding = binding;

err = gen_pool_add_owner(binding->chunk_pool, dma_addr, @@ -313,7 +319,7 @@ net_devmem_bind_dmabuf(struct net_device *dev, void *vdev, page_pool_set_dma_addr_netmem(net_iov_to_netmem(niov), net_devmem_get_dma_addr(niov)); if (direction == DMA_TO_DEVICE)

• 		binding->tx_vec[owner->area.base_virtual / PAGE_SIZE + i] = niov;
  

• 		binding->tx_vec[(owner->area.base_virtual >> niov_shift) + i] = niov;
  

  }

virtual += len; @@ -430,13 +436,15 @@ struct net_iov * net_devmem_get_niov_at(struct net_devmem_dmabuf_binding *binding, size_t virt_addr, size_t *off, size_t *size) {

• size_t niov_size = 1UL << binding->niov_shift;
• if (virt_addr >= binding->dmabuf->size) return NULL;

• *off = virt_addr % PAGE_SIZE;
• *size = PAGE_SIZE - *off;

• *off = virt_addr & (niov_size - 1);
• *size = niov_size - *off;

• return binding->tx_vec[virt_addr / PAGE_SIZE];

• return binding->tx_vec[virt_addr >> binding->niov_shift];

} /*** "Dmabuf devmem memory provider" ***/ @@ -454,8 +462,8 @@ int mp_dmabuf_devmem_init(struct page_pool *pool) pool->dma_sync = false; pool->dma_sync_for_cpu = false;

• if (pool->p.order != 0)

• return -E2BIG;
  

• if (pool->p.order != binding->niov_shift - PAGE_SHIFT)

• return -EINVAL;
  

Any specific reason you change E2BIG to EINVAL?