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Date: Thu, 17 Oct 2019 10:29:01 +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 08/10 net-next] page_pool: Add statistics
On Wed, 16 Oct 2019 15:50:26 -0700
Jonathan Lemon <jonathan.lemon@...il.com> wrote:
> Add statistics to the page pool, providing visibility into its operation.
>
> Callers can provide a location where the stats are stored, otherwise
> the page pool will allocate a statistic area.
>
> Signed-off-by: Jonathan Lemon <jonathan.lemon@...il.com>
> ---
> include/net/page_pool.h | 21 +++++++++++++---
> net/core/page_pool.c | 55 +++++++++++++++++++++++++++++++++++------
> 2 files changed, 65 insertions(+), 11 deletions(-)
>
> diff --git a/include/net/page_pool.h b/include/net/page_pool.h
> index fc340db42f9a..4f383522b141 100644
> --- a/include/net/page_pool.h
> +++ b/include/net/page_pool.h
> @@ -34,8 +34,11 @@
> #include <linux/ptr_ring.h>
> #include <linux/dma-direction.h>
>
> -#define PP_FLAG_DMA_MAP 1 /* Should page_pool do the DMA map/unmap */
> -#define PP_FLAG_ALL PP_FLAG_DMA_MAP
> +#define PP_FLAG_DMA_MAP BIT(0) /* page_pool does the DMA map/unmap */
> +#define PP_FLAG_ALL (PP_FLAG_DMA_MAP)
> +
> +/* internal flags, not expoed to user */
> +#define PP_FLAG_INTERNAL_STATS BIT(8)
>
> /*
> * Fast allocation side cache array/stack
> @@ -57,6 +60,17 @@
> #define PP_ALLOC_POOL_DEFAULT 1024
> #define PP_ALLOC_POOL_LIMIT 32768
>
> +struct page_pool_stats {
> + u64 cache_hit;
> + u64 cache_full;
> + u64 cache_empty;
> + u64 ring_produce;
> + u64 ring_consume;
You are placing producer and consumer counters on the same cache-line.
This is not acceptable.
The page pool and ptr_ring, are specifically designed to avoid
cache-line contention between consumers and producers. This patch
kills that work.
> + u64 ring_return;
> + u64 flush;
> + u64 node_change;
> +};
Another example of carefully avoiding cache-line bouncing is the
inflight tracking, e.g. the struct placement of pages_state_release_cnt
and pages_state_hold_cnt for inflight accounting.
> +
> struct page_pool_params {
> unsigned int flags;
> unsigned int order;
> @@ -65,6 +79,7 @@ struct page_pool_params {
> int nid; /* Numa node id to allocate from pages from */
> enum dma_data_direction dma_dir; /* DMA mapping direction */
> struct device *dev; /* device, for DMA pre-mapping purposes */
> + struct page_pool_stats *stats; /* pool stats stored externally */
> };
>
> struct page_pool {
> @@ -230,8 +245,8 @@ static inline bool page_pool_put(struct page_pool *pool)
> static inline void page_pool_update_nid(struct page_pool *pool, int new_nid)
> {
> if (unlikely(pool->p.nid != new_nid)) {
> - /* TODO: Add statistics/trace */
> pool->p.nid = new_nid;
> + pool->p.stats->node_change++;
> }
> }
> #endif /* _NET_PAGE_POOL_H */
> diff --git a/net/core/page_pool.c b/net/core/page_pool.c
> index f8fedecddb6f..ea6202813584 100644
> --- a/net/core/page_pool.c
> +++ b/net/core/page_pool.c
> @@ -20,9 +20,10 @@
>
> static int page_pool_init(struct page_pool *pool)
> {
> + int size;
>
> /* Validate only known flags were used */
> - if (pool->p.flags & ~(PP_FLAG_ALL))
> + if (pool->p.flags & ~PP_FLAG_ALL)
> return -EINVAL;
>
> if (!pool->p.pool_size)
> @@ -40,8 +41,16 @@ static int page_pool_init(struct page_pool *pool)
> (pool->p.dma_dir != DMA_BIDIRECTIONAL))
> return -EINVAL;
>
> + if (!pool->p.stats) {
> + size = sizeof(struct page_pool_stats);
> + pool->p.stats = kzalloc_node(size, GFP_KERNEL, pool->p.nid);
> + if (!pool->p.stats)
> + return -ENOMEM;
> + pool->p.flags |= PP_FLAG_INTERNAL_STATS;
> + }
> +
> if (ptr_ring_init(&pool->ring, pool->p.pool_size, GFP_KERNEL) < 0)
> - return -ENOMEM;
> + goto fail;
>
> atomic_set(&pool->pages_state_release_cnt, 0);
>
> @@ -52,6 +61,12 @@ static int page_pool_init(struct page_pool *pool)
> get_device(pool->p.dev);
>
> return 0;
> +
> +fail:
> + if (pool->p.flags & PP_FLAG_INTERNAL_STATS)
> + kfree(pool->p.stats);
> +
> + return -ENOMEM;
> }
>
> struct page_pool *page_pool_create(const struct page_pool_params *params)
> @@ -98,9 +113,11 @@ static struct page *__page_pool_get_cached(struct page_pool *pool)
> if (likely(in_serving_softirq())) {
> if (likely(pool->alloc_count)) {
> /* Fast-path */
> + pool->p.stats->cache_hit++;
> page = pool->alloc_cache[--pool->alloc_count];
> return page;
> }
> + pool->p.stats->cache_empty++;
> refill = true;
> }
>
> @@ -113,10 +130,13 @@ static struct page *__page_pool_get_cached(struct page_pool *pool)
> */
> spin_lock(&r->consumer_lock);
> page = __ptr_ring_consume(r);
> - if (refill)
> + if (refill) {
> pool->alloc_count = __ptr_ring_consume_batched(r,
> pool->alloc_cache,
> PP_ALLOC_CACHE_REFILL);
> + pool->p.stats->ring_consume += pool->alloc_count;
> + }
> + pool->p.stats->ring_consume += !!page;
> spin_unlock(&r->consumer_lock);
> return page;
> }
> @@ -266,15 +286,23 @@ static void __page_pool_return_page(struct page_pool *pool, struct page *page)
> static bool __page_pool_recycle_into_ring(struct page_pool *pool,
> struct page *page)
> {
> + struct ptr_ring *r = &pool->ring;
> int ret;
>
> - /* BH protection not needed if current is serving softirq */
> if (in_serving_softirq())
> - ret = ptr_ring_produce(&pool->ring, page);
> + spin_lock(&r->producer_lock);
> else
> - ret = ptr_ring_produce_bh(&pool->ring, page);
> + spin_lock_bh(&r->producer_lock);
>
> - return (ret == 0) ? true : false;
> + ret = __ptr_ring_produce(r, page);
> + pool->p.stats->ring_produce++;
> +
> + if (in_serving_softirq())
> + spin_unlock(&r->producer_lock);
> + else
> + spin_unlock_bh(&r->producer_lock);
> +
> + return ret == 0;
> }
>
> /* Only allow direct recycling in special circumstances, into the
> @@ -285,8 +313,10 @@ 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 == pool->p.cache_size))
> + if (unlikely(pool->alloc_count == pool->p.cache_size)) {
> + pool->p.stats->cache_full++;
> return false;
> + }
>
> /* Caller MUST have verified/know (page_ref_count(page) == 1) */
> pool->alloc_cache[pool->alloc_count++] = page;
> @@ -343,6 +373,7 @@ EXPORT_SYMBOL(__page_pool_put_page);
> static void __page_pool_empty_ring(struct page_pool *pool)
> {
> struct page *page;
> + int count = 0;
>
> /* Empty recycle ring */
> while ((page = ptr_ring_consume_bh(&pool->ring))) {
> @@ -351,8 +382,11 @@ static void __page_pool_empty_ring(struct page_pool *pool)
> pr_crit("%s() page_pool refcnt %d violation\n",
> __func__, page_ref_count(page));
>
> + count++;
> __page_pool_return_page(pool, page);
> }
> +
> + pool->p.stats->ring_return += count;
> }
>
> static void __warn_in_flight(struct page_pool *pool)
> @@ -381,6 +415,9 @@ void __page_pool_free(struct page_pool *pool)
> if (!__page_pool_safe_to_destroy(pool))
> __warn_in_flight(pool);
>
> + if (pool->p.flags & PP_FLAG_INTERNAL_STATS)
> + kfree(pool->p.stats);
> +
> ptr_ring_cleanup(&pool->ring, NULL);
>
> if (pool->p.flags & PP_FLAG_DMA_MAP)
> @@ -394,6 +431,8 @@ static void page_pool_flush(struct page_pool *pool)
> {
> struct page *page;
>
> + pool->p.stats->flush++;
> +
> /* Empty alloc cache, assume caller made sure this is
> * no-longer in use, and page_pool_alloc_pages() cannot be
> * called concurrently.
Have you benchmarked the overhead of adding this accounting?
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer
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