linux-kernel - Re: [RFC PATCH 2/5] tcp: add TCP support for low latency receive poll.

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Message-ID: <1362503593.2791.36.camel@bwh-desktop.uk.solarflarecom.com>
Date:	Tue, 5 Mar 2013 17:13:13 +0000
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Eliezer Tamir <eliezer.tamir@...ux.jf.intel.com>
CC:	<linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>,
	Dave Miller <davem@...emloft.net>,
	Jesse Brandeburg <jesse.brandeburg@...el.com>,
	<e1000-devel@...ts.sourceforge.net>,
	Willem de Bruijn <willemb@...gle.com>,
	Andi Kleen <andi@...stfloor.org>, HPA <hpa@...or.com>,
	Eliezer Tamir <eliezer@...ir.org.il>
Subject: Re: [RFC PATCH 2/5] tcp: add TCP support for low latency receive
 poll.

On Wed, 2013-02-27 at 09:56 -0800, Eliezer Tamir wrote:
> an example of how one could add support for ndo_ll_poll to TCP.
[...]
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -279,6 +279,7 @@
>  
>  #include <asm/uaccess.h>
>  #include <asm/ioctls.h>
> +#include <net/ll_poll.h>
>  
>  int sysctl_tcp_fin_timeout __read_mostly = TCP_FIN_TIMEOUT;
>  
> @@ -1475,6 +1476,17 @@ int tcp_read_sock(struct sock *sk, read_descriptor_t *desc,
>  
>  	if (sk->sk_state == TCP_LISTEN)
>  		return -ENOTCONN;
> +
> +#ifdef CONFIG_INET_LL_TCP_POLL
> +/* TODO: what do we do if the state changes after sk_poll_ll()? */

Maybe this bit should be a separate function that the callers can use
(or not) before calling tcp_read_sock().  Then they must take care of
re-locking and revalidating if it decides to poll.

Ben.

> +	if (sk_valid_ll(sk) && skb_queue_empty(&sk->sk_receive_queue)
> +		&& (sk->sk_state == TCP_ESTABLISHED)) {
> +
> +		release_sock(sk);
> +		sk_poll_ll(sk);
> +		lock_sock(sk);
> +	}
> +#endif
>  	while ((skb = tcp_recv_skb(sk, seq, &offset)) != NULL) {
>  		if (offset < skb->len) {
>  			int used;
[...]

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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