linux-kernel - Re: [PATCH v3 net-next 1/4] net: implement support for low latency socket polling

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Message-ID: <1369063764.3301.182.camel@edumazet-glaptop>
Date:	Mon, 20 May 2013 08:29:24 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Eliezer Tamir <eliezer.tamir@...ux.intel.com>
Cc:	Dave 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>,
	Andi Kleen <andi@...stfloor.org>, HPA <hpa@...or.com>,
	Eliezer Tamir <eliezer@...ir.org.il>
Subject: Re: [PATCH v3 net-next 1/4] net: implement support for low latency
 socket polling

On Mon, 2013-05-20 at 13:16 +0300, Eliezer Tamir wrote:
> Adds a new ndo_ll_poll method and the code that supports and uses it.
> This method can be used by low latency applications to busy poll ethernet
> device queues directly from the socket code. The ip_low_latency_poll sysctl
> entry controls how many cycles to poll. Set to zero to disable.
> 

This changelog lacks a lot of information, see below.

Part of this information was in your 0/4 text, but it wont be included
in the git tree.

> Signed-off-by: Alexander Duyck <alexander.h.duyck@...el.com>
> Signed-off-by: Jesse Brandeburg <jesse.brandeburg@...el.com>
> Tested-by: Willem de Bruijn <willemb@...gle.com>
> Signed-off-by: Eliezer Tamir <eliezer.tamir@...ux.intel.com>
> ---
> 

> +
> +static inline void skb_mark_ll(struct sk_buff *skb, struct napi_struct *napi)
> +{
> +	skb->dev_ref = napi;
> +}
> +
> +static inline void sk_mark_ll(struct sock *sk, struct sk_buff *skb)
> +{
> +	sk->dev_ref = skb->dev_ref;
> +}

I do not see why it's safe to keep a pointer to a napi object without
taking a reference, or something to prevent object being removed.

Using a genid might be enough. (some counter incremented every time a
napi is dismantled)

Alternatively, use a napi_id instead of a pointer.



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