Message-ID: <1369142926.3301.213.camel@edumazet-glaptop>
Subject: Re: [PATCH v3 net-next 1/4] net: implement support for low latency
 socket polling
From: Eric Dumazet <eric.dumazet@gmail.com>
To: Eliezer Tamir <eliezer.tamir@linux.intel.com>
Cc: Dave Miller <davem@davemloft.net>, linux-kernel@vger.kernel.org,
        netdev@vger.kernel.org, Jesse Brandeburg <jesse.brandeburg@intel.com>,
        Don Skidmore <donald.c.skidmore@intel.com>,
        e1000-devel@lists.sourceforge.net,
        Willem de Bruijn <willemb@google.com>,
        Andi Kleen <andi@firstfloor.org>, HPA <hpa@zytor.com>,
        Eliezer Tamir <eliezer@tamir.org.il>
Date: Tue, 21 May 2013 06:28:46 -0700
In-Reply-To: <519B2237.20204@linux.intel.com>
References: <20130520101552.14133.45953.stgit@ladj378.jer.intel.com>
	  <20130520101601.14133.874.stgit@ladj378.jer.intel.com>
	 <1369063764.3301.182.camel@edumazet-glaptop>
	 <519B2237.20204@linux.intel.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 7bit
Mime-Version: 1.0
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1756
Lines: 51

On Tue, 2013-05-21 at 10:28 +0300, Eliezer Tamir wrote:
> On 20/05/2013 18:29, Eric Dumazet wrote:
> > On Mon, 2013-05-20 at 13:16 +0300, Eliezer Tamir wrote:
> ---
> >> +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)
> 
> I really like this approach and I tried it.
> The main problem I had is that you need to increase the size of the skb 
> to store the generation id unless you stuff it in the flags2 bitfield.
> There appear to be only 7 useful bit left there.
> Is it OK to use them all up?
> 
> 
> > 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.


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/