linux-kernel - Re: [PATCH v9 net-next 2/7] net: add low latency socket poll

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Date:	Wed, 05 Jun 2013 08:21:54 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Eliezer Tamir <eliezer.tamir@...ux.intel.com>
Cc:	David Miller <davem@...emloft.net>, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org,
	Jesse Brandeburg <jesse.brandeburg@...el.com>,
	Don Skidmore <donald.c.skidmore@...el.com>,
	e1000-devel@...ts.sourceforge.net,
	Willem de Bruijn <willemb@...gle.com>,
	Ben Hutchings <bhutchings@...arflare.com>,
	Andi Kleen <andi@...stfloor.org>, HPA <hpa@...or.com>,
	Eilon Greenstien <eilong@...adcom.com>,
	Or Gerlitz <or.gerlitz@...il.com>,
	Amir Vadai <amirv@...lanox.com>,
	Eliezer Tamir <eliezer@...ir.org.il>
Subject: Re: [PATCH v9 net-next 2/7] net: add low latency socket poll

On Wed, 2013-06-05 at 13:34 +0300, Eliezer Tamir wrote:


This is probably too big to be inlined, and nonblock should be a bool


It would also make sense to give end_time as a parameter, so that the
polling() code could really give  a end_time for the whole duration of
poll().

(You then should test can_poll_ll(end_time) _before_ call to
ndo_ll_poll())


> +static inline bool sk_poll_ll(struct sock *sk, int nonblock)
> +{
> +	cycles_t end_time = ll_end_time();
> +	const struct net_device_ops *ops;
> +	struct napi_struct *napi;
> +	int rc = false;
> +
> +	/*
> +	 * rcu read lock for napi hash
> +	 * bh so we don't race with net_rx_action
> +	 */
> +	rcu_read_lock_bh();
> +
> +	napi = napi_by_id(sk->sk_napi_id);
> +	if (!napi)
> +		goto out;
> +
> +	ops = napi->dev->netdev_ops;
> +	if (!ops->ndo_ll_poll)
> +		goto out;
> +
> +	do {
> +
> +		rc = ops->ndo_ll_poll(napi);
> +
> +		if (rc == LL_FLUSH_FAILED)
> +			break; /* permanent failure */
> +
> +		if (rc > 0)
> +			/* local bh are disabled so it is ok to use _BH */
> +			NET_ADD_STATS_BH(sock_net(sk),
> +					 LINUX_MIB_LOWLATENCYRXPACKETS, rc);
> +
> +	} while (skb_queue_empty(&sk->sk_receive_queue)
> +			&& can_poll_ll(end_time) && !nonblock);
> +
> +	rc = !skb_queue_empty(&sk->sk_receive_queue);
> +out:
> +	rcu_read_unlock_bh();
> +	return rc;
> +}



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