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

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Message-ID: <alpine.GSO.2.00.1305211855120.9230@git.silcnet.org>
Date:	Tue, 21 May 2013 19:02:19 +0200 (CEST)
From:	Pekka Riikonen <priikone@....fi>
To:	Eric Dumazet <eric.dumazet@...il.com>
cc:	Eliezer Tamir <eliezer.tamir@...ux.intel.com>,
	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 Tue, 21 May 2013, Eric Dumazet wrote:

: > > Alternatively, use a napi_id instead of a pointer.
: > 
: > I'm not sure I understand what you propose.
: 
: Oh well.
: 
: To get a pointer to a struct net_device, we can use ifindex, and do a
: rcu lookup into a hash table to get the net_device. We do not need
: {pointer,ifindex} but {ifindex} is enough
: 
: My suggestion is to not have skb->skb_ref but skb->napi_index : Its safe
: to copy its value from skb->napi_index to sk->napi_index without
: refcounting.
: 
: All NAPI need to get a unique napi_index, and be inserted in a hash
: table for immediate/fast lookup.
: 
Maybe even that's not needed.  Couldn't skb->queue_mapping give the 
correct NAPI instance in multiqueue nics?  The NAPI instance could be made 
easily available from skb->dev.  In any case an index is much better than 
a new pointer.

	Pekka
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