netdev - Re: [PATCH net-next] net: page_pool: optimize page pool page allocation in NUMA scenario

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Date:   Mon, 27 Jun 2022 11:50:44 +0200
From:   Jesper Dangaard Brouer <jbrouer@...hat.com>
To:     Guangbin Huang <huangguangbin2@...wei.com>, hawk@...nel.org,
        ilias.apalodimas@...aro.org, davem@...emloft.net, kuba@...nel.org,
        edumazet@...gle.com, pabeni@...hat.com
Cc:     brouer@...hat.com, lorenzo@...nel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
        lipeng321@...wei.com, chenhao288@...ilicon.com
Subject: Re: [PATCH net-next] net: page_pool: optimize page pool page
 allocation in NUMA scenario



On 24/06/2022 11.36, Guangbin Huang wrote:
> From: Jie Wang <wangjie125@...wei.com>
> 
> Currently NIC packet receiving performance based on page pool deteriorates
> occasionally. To analysis the causes of this problem page allocation stats
> are collected. Here are the stats when NIC rx performance deteriorates:
> 
> bandwidth(Gbits/s)		16.8		6.91
> rx_pp_alloc_fast		13794308	21141869
> rx_pp_alloc_slow		108625		166481
> rx_pp_alloc_slow_h		0		0
> rx_pp_alloc_empty		8192		8192
> rx_pp_alloc_refill		0		0
> rx_pp_alloc_waive		100433		158289
> rx_pp_recycle_cached		0		0
> rx_pp_recycle_cache_full	0		0
> rx_pp_recycle_ring		362400		420281
> rx_pp_recycle_ring_full		6064893		9709724
> rx_pp_recycle_released_ref	0		0
> 
> The rx_pp_alloc_waive count indicates that a large number of pages' numa
> node are inconsistent with the NIC device numa node. Therefore these pages
> can't be reused by the page pool. As a result, many new pages would be
> allocated by __page_pool_alloc_pages_slow which is time consuming. This
> causes the NIC rx performance fluctuations.
> 
> The main reason of huge numa mismatch pages in page pool is that page pool
> uses alloc_pages_bulk_array to allocate original pages. This function is
> not suitable for page allocation in NUMA scenario. So this patch uses
> alloc_pages_bulk_array_node which has a NUMA id input parameter to ensure
> the NUMA consistent between NIC device and allocated pages.
> 
> Repeated NIC rx performance tests are performed 40 times. NIC rx bandwidth
> is higher and more stable compared to the datas above. Here are three test
> stats, the rx_pp_alloc_waive count is zero and rx_pp_alloc_slow which
> indicates pages allocated from slow patch is relatively low.
> 
> bandwidth(Gbits/s)		93		93.9		93.8
> rx_pp_alloc_fast		60066264	61266386	60938254
> rx_pp_alloc_slow		16512		16517		16539
> rx_pp_alloc_slow_ho		0		0		0
> rx_pp_alloc_empty		16512		16517		16539
> rx_pp_alloc_refill		473841		481910		481585
> rx_pp_alloc_waive		0		0		0
> rx_pp_recycle_cached		0		0		0
> rx_pp_recycle_cache_full	0		0		0
> rx_pp_recycle_ring		29754145	30358243	30194023
> rx_pp_recycle_ring_full		0		0		0
> rx_pp_recycle_released_ref	0		0		0
> 
> Signed-off-by: Jie Wang <wangjie125@...wei.com>
> ---
>   net/core/page_pool.c | 11 ++++++++++-
>   1 file changed, 10 insertions(+), 1 deletion(-)

Thanks for improving this, but we need some small adjustments below.
And then you need to send a V2 of the patch.

> diff --git a/net/core/page_pool.c b/net/core/page_pool.c
> index f18e6e771993..15997fcd78f3 100644
> --- a/net/core/page_pool.c
> +++ b/net/core/page_pool.c
> @@ -377,6 +377,7 @@ static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool,
>   	unsigned int pp_order = pool->p.order;
>   	struct page *page;
>   	int i, nr_pages;
> +	int pref_nid; /* preferred NUMA node */
>   
>   	/* Don't support bulk alloc for high-order pages */
>   	if (unlikely(pp_order))
> @@ -386,10 +387,18 @@ static struct page *__page_pool_alloc_pages_slow(struct page_pool *pool,
>   	if (unlikely(pool->alloc.count > 0))
>   		return pool->alloc.cache[--pool->alloc.count];
>   
> +#ifdef CONFIG_NUMA
> +	pref_nid = (pool->p.nid == NUMA_NO_NODE) ? numa_mem_id() : pool->p.nid;
> +#else
> +	/* Ignore pool->p.nid setting if !CONFIG_NUMA, helps compiler */

Remove "helps compiler" from comments, it only make sense in the code
this was copy-pasted from.


> +	pref_nid = numa_mem_id(); /* will be zero like page_to_nid() */

The comment about "page_to_nid()" is only relevant in the code
this was copy-pasted from.

Change to:
	pref_nid = NUMA_NO_NODE;

As alloc_pages_bulk_array_node() will be inlined, the effect (generated 
asm code) will be the same, but it will be better for code maintenance.

> +#endif
> +
>   	/* Mark empty alloc.cache slots "empty" for alloc_pages_bulk_array */
>   	memset(&pool->alloc.cache, 0, sizeof(void *) * bulk);
>   
> -	nr_pages = alloc_pages_bulk_array(gfp, bulk, pool->alloc.cache);
> +	nr_pages = alloc_pages_bulk_array_node(gfp, pref_nid, bulk,
> +					       pool->alloc.cache);
>   	if (unlikely(!nr_pages))
>   		return NULL;
>