netdev - Re: [PATCH net-next] pktgen: Add NOINIT option to leave packet data uninitialized

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Message-ID: <1400252935.7973.176.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Fri, 16 May 2014 08:08:55 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Thomas Graf <tgraf@...g.ch>
Cc:	Ben Greear <greearb@...delatech.com>, davem@...emloft.net,
	netdev@...r.kernel.org
Subject: Re: [PATCH net-next] pktgen: Add NOINIT option to leave packet data
 uninitialized

On Fri, 2014-05-16 at 15:50 +0100, Thomas Graf wrote:
> On 05/16/14 at 07:23am, Eric Dumazet wrote:
> > pktgen has already a way to send fragments which are not memset for
> > every packet. We share a 'zero' page for that.
> > 
> > So only headers need to be really built for each packet.
> 
> Right, F_NOINIT is exclusively for cases where a linear buffer is
> desired. I don't fully understand the argument of exposing kernel
> memory as root considering the presence of /dev/mem though.
> 
> That said, I understand that this is a special case and that the
> objective is reachable with non linear skbs already so I'm fine
> with ignoring this patch and have it linger outside of the tree for
> whoever has use for it.

Note that if you really want to save cpu cycles, you might simply avoid
kfree_skb()/alloc_skb() pair, and reuse the previous skb.

Yes, pktgen can vary the skb->len, but this doesn't mean we can
allocate/reserve a big skb->head. Then the cost of initial memset() for
this skb is peanuts.

Synch with Jesper because he is trying to save the atomic on skb->users.



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