netdev - Re: [PATCH net-next 1/2] xsk: avoid using heavy lock when the pool is not shared

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Message-ID: <20251028172903.677f46ba@kernel.org>
Date: Tue, 28 Oct 2025 17:29:03 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Jason Xing <kerneljasonxing@...il.com>
Cc: davem@...emloft.net, edumazet@...gle.com, pabeni@...hat.com,
 bjorn@...nel.org, magnus.karlsson@...el.com, maciej.fijalkowski@...el.com,
 jonathan.lemon@...il.com, sdf@...ichev.me, ast@...nel.org,
 daniel@...earbox.net, hawk@...nel.org, john.fastabend@...il.com,
 horms@...nel.org, andrew+netdev@...n.ch, bpf@...r.kernel.org,
 netdev@...r.kernel.org, Jason Xing <kernelxing@...cent.com>
Subject: Re: [PATCH net-next 1/2] xsk: avoid using heavy lock when the pool
 is not shared

On Sat, 25 Oct 2025 14:53:09 +0800 Jason Xing wrote:
>  static int xsk_cq_reserve_locked(struct xsk_buff_pool *pool)
>  {
> +	bool lock = !list_is_singular(&pool->xsk_tx_list);
>  	unsigned long flags;
>  	int ret;
>  
> -	spin_lock_irqsave(&pool->cq_lock, flags);
> +	if (lock)
> +		spin_lock_irqsave(&pool->cq_lock, flags);
>  	ret = xskq_prod_reserve(pool->cq);
> -	spin_unlock_irqrestore(&pool->cq_lock, flags);
> +	if (lock)
> +		spin_unlock_irqrestore(&pool->cq_lock, flags);

Please explain in the commit message what guarantees that the list will
remain singular until the function exits.
-- 
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