netdev - Re: [PATCH RFC net-next] pktgen: introduce 'rx' mode

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Message-ID: <55417075.9010601@plumgrid.com>
Date:	Wed, 29 Apr 2015 16:59:49 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Daniel Borkmann <daniel@...earbox.net>,
	Thomas Graf <tgraf@...g.ch>,
	Jamal Hadi Salim <jhs@...atatu.com>,
	John Fastabend <john.r.fastabend@...el.com>,
	netdev@...r.kernel.org
Subject: Re: [PATCH RFC net-next] pktgen: introduce 'rx' mode

On 4/29/15 4:39 PM, Eric Dumazet wrote:
>
> Zap the 'burst/clone' thing, this is not going to work for RX.
> TX was okay, not RX.
>
> You could for instance do :
>
> atomic_inc(&skb->users);
> netif_receive_skb(skb);
> if (atomic_read(skb->users) != 1) {
> 	/* This is too bad, I can not recycle this skb because it is still used */
> 	consume_skb(skb);
> 	/* allocate a fresh new skb */
> 	skb = ...
> } else {
> 	/* Yeah ! Lets celebrate, cost of reusing this skb was one atomic op */
> }

ahh, great! I think I'm starting to understand.
then the following should be ok as well?

atomic_add(burst, &skb->users);
do {
    netif_receive_skb(skb);
    if (atomic_read(skb->users) != burst) {
  	/* too bad, can not recycle */
         atomic_sub(burst - 1, &skb->users);
  	consume_skb(skb);
  	/* allocate a fresh new skb */
  	skb = ...
         /* and get out of this loop */
    } else {
	/* Yeah ! the cost of reusing this skb was
            one atomic op amortized over 'burst' iterations */
    }
} while (--burst > 0);

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