Re: [PATCH net-next v10 11/14] tcp: RX path for devmem TCP

On Thu, 2024-05-30 at 20:16 +0000, Mina Almasry wrote:

@@ -2317,6 +2318,213 @@ static int tcp_inq_hint(struct sock *sk) return inq; } +/* batch __xa_alloc() calls and reduce xa_lock()/xa_unlock() overhead. */ +struct tcp_xa_pool {

• u8 max; /* max <= MAX_SKB_FRAGS */
• u8 idx; /* idx <= max */
• __u32 tokens[MAX_SKB_FRAGS];
• netmem_ref netmems[MAX_SKB_FRAGS];

+};

+static void tcp_xa_pool_commit(struct sock *sk, struct tcp_xa_pool *p,

• 	       bool lock)
  

+{

• int i;
• if (!p->max)

• return;
  

• if (lock)

• xa_lock_bh(&sk->sk_user_frags);
  

The conditional lock here confuses sparse.

I think you can avoid it providing a unlocked version (no need to check for '!p->max' the only caller wanting the unlocked version already performs such check) and a locked one, calling the other.

Cheers,

Paolo