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Subject: Re: [PATCH net-next v10 11/14] tcp: RX path for devmem TCP
From: Paolo Abeni <pabeni@redhat.com>
To: Mina Almasry <almasrymina@google.com>, netdev@vger.kernel.org, 
	linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, 
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Cc: "David S. Miller" <davem@davemloft.net>, Eric Dumazet
 <edumazet@google.com>,  Jakub Kicinski <kuba@kernel.org>, Donald Hunter
 <donald.hunter@gmail.com>, Jonathan Corbet <corbet@lwn.net>, Richard
 Henderson <richard.henderson@linaro.org>, Ivan Kokshaysky
 <ink@jurassic.park.msu.ru>, Matt Turner <mattst88@gmail.com>, Thomas
 Bogendoerfer <tsbogend@alpha.franken.de>, "James E.J. Bottomley"
 <James.Bottomley@HansenPartnership.com>, Helge Deller <deller@gmx.de>, 
 Andreas Larsson <andreas@gaisler.com>, Jesper Dangaard Brouer
 <hawk@kernel.org>, Ilias Apalodimas <ilias.apalodimas@linaro.org>, Steven
 Rostedt <rostedt@goodmis.org>, Masami Hiramatsu <mhiramat@kernel.org>,
 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>, Arnd Bergmann
 <arnd@arndb.de>, Alexei Starovoitov <ast@kernel.org>, Daniel Borkmann
 <daniel@iogearbox.net>, Andrii Nakryiko <andrii@kernel.org>, Martin KaFai
 Lau <martin.lau@linux.dev>, Eduard Zingerman <eddyz87@gmail.com>, Song Liu
 <song@kernel.org>, Yonghong Song <yonghong.song@linux.dev>, John Fastabend
 <john.fastabend@gmail.com>, KP Singh <kpsingh@kernel.org>, Stanislav
 Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>, Jiri Olsa
 <jolsa@kernel.org>,  Steffen Klassert <steffen.klassert@secunet.com>,
 Herbert Xu <herbert@gondor.apana.org.au>, David Ahern <dsahern@kernel.org>,
 Willem de Bruijn <willemdebruijn.kernel@gmail.com>,  Shuah Khan
 <shuah@kernel.org>, Sumit Semwal <sumit.semwal@linaro.org>, Christian
 =?ISO-8859-1?Q?K=F6nig?= <christian.koenig@amd.com>, Pavel Begunkov
 <asml.silence@gmail.com>, David Wei <dw@davidwei.uk>, Jason Gunthorpe
 <jgg@ziepe.ca>, Yunsheng Lin <linyunsheng@huawei.com>, Shailend Chand
 <shailend@google.com>, Harshitha Ramamurthy <hramamurthy@google.com>,
 Shakeel Butt <shakeel.butt@linux.dev>, Jeroen de Borst
 <jeroendb@google.com>, Praveen Kaligineedi <pkaligineedi@google.com>,
 Willem de Bruijn <willemb@google.com>, Kaiyuan Zhang <kaiyuanz@google.com>
Date: Tue, 04 Jun 2024 12:53:35 +0200
In-Reply-To: <20240530201616.1316526-12-almasrymina@google.com>
References: <20240530201616.1316526-1-almasrymina@google.com>
	 <20240530201616.1316526-12-almasrymina@google.com>
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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;
>  }
> =20
> +/* batch __xa_alloc() calls and reduce xa_lock()/xa_unlock() overhead. *=
/
> +struct tcp_xa_pool {
> +	u8		max; /* max <=3D MAX_SKB_FRAGS */
> +	u8		idx; /* idx <=3D 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