netdev - Re: [RFC net-next] net: page_pool: fix recycle stats for percpu page

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Message-ID: <bff45ab9-2818-4b37-837e-f18ffcab8f47@intel.com>
Date: Thu, 15 Feb 2024 14:41:52 +0100
From: Alexander Lobakin <aleksander.lobakin@...el.com>
To: Lorenzo Bianconi <lorenzo@...nel.org>
CC: <netdev@...r.kernel.org>, <lorenzo.bianconi@...hat.com>,
	<kuba@...nel.org>, <davem@...emloft.net>, <edumazet@...gle.com>,
	<pabeni@...hat.com>, <hawk@...nel.org>, <ilias.apalodimas@...aro.org>,
	<linyunsheng@...wei.com>, <toke@...hat.com>
Subject: Re: [RFC net-next] net: page_pool: fix recycle stats for percpu
 page_pool allocator

From: Lorenzo Bianconi <lorenzo@...nel.org>
Date: Wed, 14 Feb 2024 19:08:40 +0100

> Use global page_pool_recycle_stats percpu counter for percpu page_pool
> allocator.
> 
> Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
> ---
>  net/core/page_pool.c | 18 +++++++++++++-----
>  1 file changed, 13 insertions(+), 5 deletions(-)
> 
> diff --git a/net/core/page_pool.c b/net/core/page_pool.c
> index 6e0753e6a95b..1bb83b6e7a61 100644
> --- a/net/core/page_pool.c
> +++ b/net/core/page_pool.c
> @@ -31,6 +31,8 @@
>  #define BIAS_MAX	(LONG_MAX >> 1)
>  
>  #ifdef CONFIG_PAGE_POOL_STATS
> +static DEFINE_PER_CPU(struct page_pool_recycle_stats, pp_recycle_stats);
> +
>  /* alloc_stat_inc is intended to be used in softirq context */
>  #define alloc_stat_inc(pool, __stat)	(pool->alloc_stats.__stat++)
>  /* recycle_stat_inc is safe to use when preemption is possible. */
> @@ -220,14 +222,19 @@ static int page_pool_init(struct page_pool *pool,
>  	pool->has_init_callback = !!pool->slow.init_callback;
>  
>  #ifdef CONFIG_PAGE_POOL_STATS
> -	pool->recycle_stats = alloc_percpu(struct page_pool_recycle_stats);
> -	if (!pool->recycle_stats)
> -		return -ENOMEM;
> +	if (cpuid < 0) {

TBH I don't like the idea of assuming that only system page_pools might
be created with cpuid >= 0.
For example, if I have an Rx queue always pinned to one CPU, I might
want to create a PP for this queue with the cpuid set already to save
some cycles when recycling. We might also reuse cpuid later for some
more optimizations or features.

Maybe add a new PP_FLAG indicating that system percpu PP stats should be
used?

> +		pool->recycle_stats = alloc_percpu(struct page_pool_recycle_stats);
> +		if (!pool->recycle_stats)
> +			return -ENOMEM;
> +	} else {
> +		pool->recycle_stats = &pp_recycle_stats;
> +	}
>  #endif
>  
>  	if (ptr_ring_init(&pool->ring, ring_qsize, GFP_KERNEL) < 0) {
>  #ifdef CONFIG_PAGE_POOL_STATS
> -		free_percpu(pool->recycle_stats);
> +		if (cpuid < 0)
> +			free_percpu(pool->recycle_stats);
>  #endif
>  		return -ENOMEM;
>  	}
> @@ -251,7 +258,8 @@ static void page_pool_uninit(struct page_pool *pool)
>  		put_device(pool->p.dev);
>  
>  #ifdef CONFIG_PAGE_POOL_STATS
> -	free_percpu(pool->recycle_stats);
> +	if (pool->cpuid < 0)
> +		free_percpu(pool->recycle_stats);
>  #endif
>  }
>  

Thanks,
Olek