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Message-ID: <84C4DADD-C1C6-4877-A4BF-82D2CCFDD885@gmail.com>
Date: Fri, 18 Oct 2019 13:31:38 -0700
From: "Jonathan Lemon" <jonathan.lemon@...il.com>
To: "Jesper Dangaard Brouer" <brouer@...hat.com>
Cc: ilias.apalodimas@...aro.org, saeedm@...lanox.com,
tariqt@...lanox.com, netdev@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH 07/10 net-next] page_pool: allow configurable linear cache
size
On 17 Oct 2019, at 1:51, Jesper Dangaard Brouer wrote:
> 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.
Will update, but there are other items that make this lost
in the noise.
>> - /*
>> - * 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.
Will fix.
>> + * 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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