Adding upstream version 6.1.76.upstream/6.1.76

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 223 insertions, 0 deletions

diff --git a/Documentation/networking/page_pool.rst b/Documentation/networking/page_pool.rst
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+.. SPDX-License-Identifier: GPL-2.0
+
+=============
+Page Pool API
+=============
+
+The page_pool allocator is optimized for the XDP mode that uses one frame
+per-page, but it can fallback on the regular page allocator APIs.
+
+Basic use involves replacing alloc_pages() calls with the
+page_pool_alloc_pages() call.  Drivers should use page_pool_dev_alloc_pages()
+replacing dev_alloc_pages().
+
+API keeps track of inflight pages, in order to let API user know
+when it is safe to free a page_pool object.  Thus, API users
+must run page_pool_release_page() when a page is leaving the page_pool or
+call page_pool_put_page() where appropriate in order to maintain correct
+accounting.
+
+API user must call page_pool_put_page() once on a page, as it
+will either recycle the page, or in case of refcnt > 1, it will
+release the DMA mapping and inflight state accounting.
+
+Architecture overview
+=====================
+
+.. code-block:: none
+
+    +------------------+
+    |       Driver     |
+    +------------------+
+            ^
+            |
+            |
+            |
+            v
+    +--------------------------------------------+
+    |                request memory              |
+    +--------------------------------------------+
+        ^                                  ^
+        |                                  |
+        | Pool empty                       | Pool has entries
+        |                                  |
+        v                                  v
+    +-----------------------+     +------------------------+
+    | alloc (and map) pages |     |  get page from cache   |
+    +-----------------------+     +------------------------+
+                                    ^                    ^
+                                    |                    |
+                                    | cache available    | No entries, refill
+                                    |                    | from ptr-ring
+                                    |                    |
+                                    v                    v
+                          +-----------------+     +------------------+
+                          |   Fast cache    |     |  ptr-ring cache  |
+                          +-----------------+     +------------------+
+
+API interface
+=============
+The number of pools created **must** match the number of hardware queues
+unless hardware restrictions make that impossible. This would otherwise beat the
+purpose of page pool, which is allocate pages fast from cache without locking.
+This lockless guarantee naturally comes from running under a NAPI softirq.
+The protection doesn't strictly have to be NAPI, any guarantee that allocating
+a page will cause no race conditions is enough.
+
+* page_pool_create(): Create a pool.
+    * flags:      PP_FLAG_DMA_MAP, PP_FLAG_DMA_SYNC_DEV
+    * order:      2^order pages on allocation
+    * pool_size:  size of the ptr_ring
+    * nid:        preferred NUMA node for allocation
+    * dev:        struct device. Used on DMA operations
+    * dma_dir:    DMA direction
+    * max_len:    max DMA sync memory size
+    * offset:     DMA address offset
+
+* page_pool_put_page(): The outcome of this depends on the page refcnt. If the
+  driver bumps the refcnt > 1 this will unmap the page. If the page refcnt is 1
+  the allocator owns the page and will try to recycle it in one of the pool
+  caches. If PP_FLAG_DMA_SYNC_DEV is set, the page will be synced for_device
+  using dma_sync_single_range_for_device().
+
+* page_pool_put_full_page(): Similar to page_pool_put_page(), but will DMA sync
+  for the entire memory area configured in area pool->max_len.
+
+* page_pool_recycle_direct(): Similar to page_pool_put_full_page() but caller
+  must guarantee safe context (e.g NAPI), since it will recycle the page
+  directly into the pool fast cache.
+
+* page_pool_release_page(): Unmap the page (if mapped) and account for it on
+  inflight counters.
+
+* page_pool_dev_alloc_pages(): Get a page from the page allocator or page_pool
+  caches.
+
+* page_pool_get_dma_addr(): Retrieve the stored DMA address.
+
+* page_pool_get_dma_dir(): Retrieve the stored DMA direction.
+
+* page_pool_put_page_bulk(): Tries to refill a number of pages into the
+  ptr_ring cache holding ptr_ring producer lock. If the ptr_ring is full,
+  page_pool_put_page_bulk() will release leftover pages to the page allocator.
+  page_pool_put_page_bulk() is suitable to be run inside the driver NAPI tx
+  completion loop for the XDP_REDIRECT use case.
+  Please note the caller must not use data area after running
+  page_pool_put_page_bulk(), as this function overwrites it.
+
+* page_pool_get_stats(): Retrieve statistics about the page_pool. This API
+  is only available if the kernel has been configured with
+  ``CONFIG_PAGE_POOL_STATS=y``. A pointer to a caller allocated ``struct
+  page_pool_stats`` structure is passed to this API which is filled in. The
+  caller can then report those stats to the user (perhaps via ethtool,
+  debugfs, etc.). See below for an example usage of this API.
+
+Stats API and structures
+------------------------
+If the kernel is configured with ``CONFIG_PAGE_POOL_STATS=y``, the API
+``page_pool_get_stats()`` and structures described below are available. It
+takes a  pointer to a ``struct page_pool`` and a pointer to a ``struct
+page_pool_stats`` allocated by the caller.
+
+The API will fill in the provided ``struct page_pool_stats`` with
+statistics about the page_pool.
+
+The stats structure has the following fields::
+
+    struct page_pool_stats {
+        struct page_pool_alloc_stats alloc_stats;
+        struct page_pool_recycle_stats recycle_stats;
+    };
+
+
+The ``struct page_pool_alloc_stats`` has the following fields:
+  * ``fast``: successful fast path allocations
+  * ``slow``: slow path order-0 allocations
+  * ``slow_high_order``: slow path high order allocations
+  * ``empty``: ptr ring is empty, so a slow path allocation was forced.
+  * ``refill``: an allocation which triggered a refill of the cache
+  * ``waive``: pages obtained from the ptr ring that cannot be added to
+    the cache due to a NUMA mismatch.
+
+The ``struct page_pool_recycle_stats`` has the following fields:
+  * ``cached``: recycling placed page in the page pool cache
+  * ``cache_full``: page pool cache was full
+  * ``ring``: page placed into the ptr ring
+  * ``ring_full``: page released from page pool because the ptr ring was full
+  * ``released_refcnt``: page released (and not recycled) because refcnt > 1
+
+Coding examples
+===============
+
+Registration
+------------
+
+.. code-block:: c
+
+    /* Page pool registration */
+    struct page_pool_params pp_params = { 0 };
+    struct xdp_rxq_info xdp_rxq;
+    int err;
+
+    pp_params.order = 0;
+    /* internal DMA mapping in page_pool */
+    pp_params.flags = PP_FLAG_DMA_MAP;
+    pp_params.pool_size = DESC_NUM;
+    pp_params.nid = NUMA_NO_NODE;
+    pp_params.dev = priv->dev;
+    pp_params.dma_dir = xdp_prog ? DMA_BIDIRECTIONAL : DMA_FROM_DEVICE;
+    page_pool = page_pool_create(&pp_params);
+
+    err = xdp_rxq_info_reg(&xdp_rxq, ndev, 0);
+    if (err)
+        goto err_out;
+
+    err = xdp_rxq_info_reg_mem_model(&xdp_rxq, MEM_TYPE_PAGE_POOL, page_pool);
+    if (err)
+        goto err_out;
+
+NAPI poller
+-----------
+
+
+.. code-block:: c
+
+    /* NAPI Rx poller */
+    enum dma_data_direction dma_dir;
+
+    dma_dir = page_pool_get_dma_dir(dring->page_pool);
+    while (done < budget) {
+        if (some error)
+            page_pool_recycle_direct(page_pool, page);
+        if (packet_is_xdp) {
+            if XDP_DROP:
+                page_pool_recycle_direct(page_pool, page);
+        } else (packet_is_skb) {
+            page_pool_release_page(page_pool, page);
+            new_page = page_pool_dev_alloc_pages(page_pool);
+        }
+    }
+
+Stats
+-----
+
+.. code-block:: c
+
+	#ifdef CONFIG_PAGE_POOL_STATS
+	/* retrieve stats */
+	struct page_pool_stats stats = { 0 };
+	if (page_pool_get_stats(page_pool, &stats)) {
+		/* perhaps the driver reports statistics with ethool */
+		ethtool_print_allocation_stats(&stats.alloc_stats);
+		ethtool_print_recycle_stats(&stats.recycle_stats);
+	}
+	#endif
+
+Driver unload
+-------------
+
+.. code-block:: c
+
+    /* Driver unload */
+    page_pool_put_full_page(page_pool, page, false);
+    xdp_rxq_info_unreg(&xdp_rxq);