Re: [PATCH net-next 1/2] page_pool: Convert page_pool_recycle_stats to u64_stats_t.

[Yunsheng Lin <linyunsheng@huawei.com>]

On 2025/2/21 19:52, Sebastian Andrzej Siewior wrote:
>  
>  static const char pp_stats[][ETH_GSTRING_LEN] = {
> @@ -82,6 +88,7 @@ static const char pp_stats[][ETH_GSTRING_LEN] = {
>  bool page_pool_get_stats(const struct page_pool *pool,
>  			 struct page_pool_stats *stats)
>  {
> +	unsigned int start;
>  	int cpu = 0;
>  
>  	if (!stats)
> @@ -99,11 +106,19 @@ bool page_pool_get_stats(const struct page_pool *pool,
>  		const struct page_pool_recycle_stats *pcpu =
>  			per_cpu_ptr(pool->recycle_stats, cpu);
>  
> -		stats->recycle_stats.cached += pcpu->cached;
> -		stats->recycle_stats.cache_full += pcpu->cache_full;
> -		stats->recycle_stats.ring += pcpu->ring;
> -		stats->recycle_stats.ring_full += pcpu->ring_full;
> -		stats->recycle_stats.released_refcnt += pcpu->released_refcnt;
> +		do {
> +			start = u64_stats_fetch_begin(&pcpu->syncp);
> +			u64_stats_add(&stats->recycle_stats.cached,
> +				      u64_stats_read(&pcpu->cached));
> +			u64_stats_add(&stats->recycle_stats.cache_full,
> +				      u64_stats_read(&pcpu->cache_full));
> +			u64_stats_add(&stats->recycle_stats.ring,
> +				      u64_stats_read(&pcpu->ring));
> +			u64_stats_add(&stats->recycle_stats.ring_full,
> +				      u64_stats_read(&pcpu->ring_full));
> +			u64_stats_add(&stats->recycle_stats.released_refcnt,
> +				      u64_stats_read(&pcpu->released_refcnt));

It seems the above u64_stats_add() may be called more than one time
if the below u64_stats_fetch_retry() returns true, which might mean
the stats is added more than it is needed.

It seems more correct to me that pool->alloc_stats is read into a
local varible in the while loop and then do the addition outside
the while loop?

> +		} while (u64_stats_fetch_retry(&pcpu->syncp, start));
>  	}
>  
>  	return true;