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Message-ID: <20191017105152.50e6ed36@carbon>
Date: Thu, 17 Oct 2019 10:51:52 +0200
From: Jesper Dangaard Brouer <brouer@...hat.com>
To: Jonathan Lemon <jonathan.lemon@...il.com>
Cc: <ilias.apalodimas@...aro.org>, <saeedm@...lanox.com>,
<tariqt@...lanox.com>, <netdev@...r.kernel.org>,
<kernel-team@...com>, brouer@...hat.com
Subject: Re: [PATCH 07/10 net-next] page_pool: allow configurable linear
cache size
On Wed, 16 Oct 2019 15:50:25 -0700
Jonathan Lemon <jonathan.lemon@...il.com> wrote:
> Some drivers may utilize more than one page per RX work entry.
> Allow a configurable cache size, with the same defaults if the
> size is zero.
>
> Convert magic numbers into descriptive entries.
>
> Re-arrange the page_pool structure for efficiency.
IMHO the re-arrange you did does not improve efficiency, it kills the
efficiency...
> Signed-off-by: Jonathan Lemon <jonathan.lemon@...il.com>
> ---
> include/net/page_pool.h | 50 ++++++++++++++++++++---------------------
> net/core/page_pool.c | 49 +++++++++++++++++++++++-----------------
> 2 files changed, 54 insertions(+), 45 deletions(-)
>
> diff --git a/include/net/page_pool.h b/include/net/page_pool.h
> index 89bc91294b53..fc340db42f9a 100644
> --- a/include/net/page_pool.h
> +++ b/include/net/page_pool.h
> @@ -51,41 +51,34 @@
> * cache is already full (or partly full) then the XDP_DROP recycles
> * would have to take a slower code path.
> */
> -#define PP_ALLOC_CACHE_SIZE 128
> #define PP_ALLOC_CACHE_REFILL 64
> -struct pp_alloc_cache {
> - u32 count;
> - void *cache[PP_ALLOC_CACHE_SIZE];
> -};
> +#define PP_ALLOC_CACHE_DEFAULT (2 * PP_ALLOC_CACHE_REFILL)
> +#define PP_ALLOC_CACHE_LIMIT 512
> +#define PP_ALLOC_POOL_DEFAULT 1024
> +#define PP_ALLOC_POOL_LIMIT 32768
>
> struct page_pool_params {
> unsigned int flags;
> unsigned int order;
> unsigned int pool_size;
> + unsigned int cache_size;
> int nid; /* Numa node id to allocate from pages from */
> - struct device *dev; /* device, for DMA pre-mapping purposes */
> enum dma_data_direction dma_dir; /* DMA mapping direction */
> + struct device *dev; /* device, for DMA pre-mapping purposes */
> };
>
> struct page_pool {
> struct page_pool_params p;
>
> + u32 alloc_count;
> u32 pages_state_hold_cnt;
> + atomic_t pages_state_release_cnt;
The struct members pages_state_hold_cnt and pages_state_release_cnt,
MUST be kept on different cachelines, else the point of tracking
inflight pages this way is lost.
> - /*
> - * Data structure for allocation side
> - *
> - * Drivers allocation side usually already perform some kind
> - * of resource protection. Piggyback on this protection, and
> - * require driver to protect allocation side.
> - *
> - * For NIC drivers this means, allocate a page_pool per
> - * RX-queue. As the RX-queue is already protected by
> - * Softirq/BH scheduling and napi_schedule. NAPI schedule
> - * guarantee that a single napi_struct will only be scheduled
> - * on a single CPU (see napi_schedule).
> + /* A page_pool is strictly tied to a single RX-queue being
> + * protected by NAPI, due to above pp_alloc_cache. This
^^^^^^^^^^^^^^
You remove the 'pp_alloc_cache' in this patch, and still mention it in
the comments.
> + * refcnt serves purpose is to simplify drivers error handling.
> */
> - struct pp_alloc_cache alloc ____cacheline_aligned_in_smp;
> + refcount_t user_cnt;
>
> /* Data structure for storing recycled pages.
> *
> @@ -100,13 +93,20 @@ struct page_pool {
> */
> struct ptr_ring ring;
>
> - atomic_t pages_state_release_cnt;
> -
> - /* A page_pool is strictly tied to a single RX-queue being
> - * protected by NAPI, due to above pp_alloc_cache. This
> - * refcnt serves purpose is to simplify drivers error handling.
> + /*
> + * Data structure for allocation side
> + *
> + * Drivers allocation side usually already perform some kind
> + * of resource protection. Piggyback on this protection, and
> + * require driver to protect allocation side.
> + *
> + * For NIC drivers this means, allocate a page_pool per
> + * RX-queue. As the RX-queue is already protected by
> + * Softirq/BH scheduling and napi_schedule. NAPI schedule
> + * guarantee that a single napi_struct will only be scheduled
> + * on a single CPU (see napi_schedule).
> */
> - refcount_t user_cnt;
> + void *alloc_cache[];
> };
>
> struct page *page_pool_alloc_pages(struct page_pool *pool, gfp_t gfp);
> diff --git a/net/core/page_pool.c b/net/core/page_pool.c
> index ea56823236c5..f8fedecddb6f 100644
> --- a/net/core/page_pool.c
> +++ b/net/core/page_pool.c
> @@ -18,22 +18,18 @@
>
> #include <trace/events/page_pool.h>
>
> -static int page_pool_init(struct page_pool *pool,
> - const struct page_pool_params *params)
> +static int page_pool_init(struct page_pool *pool)
> {
> - unsigned int ring_qsize = 1024; /* Default */
> -
> - memcpy(&pool->p, params, sizeof(pool->p));
>
> /* Validate only known flags were used */
> if (pool->p.flags & ~(PP_FLAG_ALL))
> return -EINVAL;
>
> - if (pool->p.pool_size)
> - ring_qsize = pool->p.pool_size;
> + if (!pool->p.pool_size)
> + pool->p.pool_size = PP_ALLOC_POOL_DEFAULT;
>
> /* Sanity limit mem that can be pinned down */
> - if (ring_qsize > 32768)
> + if (pool->p.pool_size > PP_ALLOC_POOL_LIMIT)
> return -E2BIG;
>
> /* DMA direction is either DMA_FROM_DEVICE or DMA_BIDIRECTIONAL.
> @@ -44,7 +40,7 @@ static int page_pool_init(struct page_pool *pool,
> (pool->p.dma_dir != DMA_BIDIRECTIONAL))
> return -EINVAL;
>
> - if (ptr_ring_init(&pool->ring, ring_qsize, GFP_KERNEL) < 0)
> + if (ptr_ring_init(&pool->ring, pool->p.pool_size, GFP_KERNEL) < 0)
> return -ENOMEM;
>
> atomic_set(&pool->pages_state_release_cnt, 0);
> @@ -61,13 +57,26 @@ static int page_pool_init(struct page_pool *pool,
> struct page_pool *page_pool_create(const struct page_pool_params *params)
> {
> struct page_pool *pool;
> + u32 cache_size, size;
> int err;
>
> - pool = kzalloc_node(sizeof(*pool), GFP_KERNEL, params->nid);
> + cache_size = params->cache_size;
> + if (!cache_size)
> + cache_size = PP_ALLOC_CACHE_DEFAULT;
> +
> + /* Sanity limit mem that can be pinned down */
> + if (cache_size > PP_ALLOC_CACHE_LIMIT)
> + return ERR_PTR(-E2BIG);
> +
> + size = sizeof(*pool) + cache_size * sizeof(void *);
> + pool = kzalloc_node(size, GFP_KERNEL, params->nid);
You have now placed alloc_cache at the end of page_pool struct, this
allows for dynamic changing the size, that is kind of nice. Before I
placed pp_alloc_cache in struct to make sure that we didn't have
false-sharing. Now, I'm unsure if false-sharing can happen?
(depend on alignment from kzalloc_node).
> if (!pool)
> return ERR_PTR(-ENOMEM);
>
> - err = page_pool_init(pool, params);
> + memcpy(&pool->p, params, sizeof(pool->p));
> + pool->p.cache_size = cache_size;
> +
> + err = page_pool_init(pool);
> if (err < 0) {
> pr_warn("%s() gave up with errno %d\n", __func__, err);
> kfree(pool);
> @@ -87,9 +96,9 @@ static struct page *__page_pool_get_cached(struct page_pool *pool)
>
> /* Test for safe-context, caller should provide this guarantee */
> if (likely(in_serving_softirq())) {
> - if (likely(pool->alloc.count)) {
> + if (likely(pool->alloc_count)) {
> /* Fast-path */
> - page = pool->alloc.cache[--pool->alloc.count];
> + page = pool->alloc_cache[--pool->alloc_count];
> return page;
> }
> refill = true;
> @@ -105,8 +114,8 @@ static struct page *__page_pool_get_cached(struct page_pool *pool)
> spin_lock(&r->consumer_lock);
> page = __ptr_ring_consume(r);
> if (refill)
> - pool->alloc.count = __ptr_ring_consume_batched(r,
> - pool->alloc.cache,
> + pool->alloc_count = __ptr_ring_consume_batched(r,
> + pool->alloc_cache,
> PP_ALLOC_CACHE_REFILL);
> spin_unlock(&r->consumer_lock);
> return page;
> @@ -276,11 +285,11 @@ static bool __page_pool_recycle_into_ring(struct page_pool *pool,
> static bool __page_pool_recycle_into_cache(struct page *page,
> struct page_pool *pool)
> {
> - if (unlikely(pool->alloc.count == PP_ALLOC_CACHE_SIZE))
> + if (unlikely(pool->alloc_count == pool->p.cache_size))
> return false;
>
> /* Caller MUST have verified/know (page_ref_count(page) == 1) */
> - pool->alloc.cache[pool->alloc.count++] = page;
> + pool->alloc_cache[pool->alloc_count++] = page;
> return true;
> }
>
> @@ -365,7 +374,7 @@ void __page_pool_free(struct page_pool *pool)
> if (!page_pool_put(pool))
> return;
>
> - WARN(pool->alloc.count, "API usage violation");
> + WARN(pool->alloc_count, "API usage violation");
> WARN(!ptr_ring_empty(&pool->ring), "ptr_ring is not empty");
>
> /* Can happen due to forced shutdown */
> @@ -389,8 +398,8 @@ static void page_pool_flush(struct page_pool *pool)
> * no-longer in use, and page_pool_alloc_pages() cannot be
> * called concurrently.
> */
> - while (pool->alloc.count) {
> - page = pool->alloc.cache[--pool->alloc.count];
> + while (pool->alloc_count) {
> + page = pool->alloc_cache[--pool->alloc_count];
> __page_pool_return_page(pool, page);
> }
>
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer
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