netdev - Re: [PATCH net-2.6] net_sched: always clone skbs

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Message-ID: <20101223230439.GB1913@del.dom.local>
Date:	Fri, 24 Dec 2010 00:04:39 +0100
From:	Jarek Poplawski <jarkao2@...il.com>
To:	jamal <hadi@...erus.ca>
Cc:	Changli Gao <xiaosuo@...il.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	Pawel Staszewski <pstaszewski@...are.pl>
Subject: Re: [PATCH net-2.6] net_sched: always clone skbs

On Thu, Dec 23, 2010 at 08:35:33AM -0500, jamal wrote:
> On Tue, 2010-12-21 at 23:37 +0100, Jarek Poplawski wrote:
> 
> > Actually, when dumb isn't a good principle? ;->
> > 
> > Speaking about wrong things like optimizing this 1st commandment: it
> > seems, if we're stealing not shared skb it's not unreasonable to tell
> > others not to touch it anymore, and skip kfree_skb() in handle_ing(),
> > unless I miss something?
> 
> I dont know how much cycles it will save you vs the code you add
> but it is not unreasonable. Of course it would mean we are moving
> beyond KISSes[1] now Jarek;->

Hmm... seeing all those multiqued multiques I thought everybody was
beyond, but no problem, let's go back to KISSes[2] ;-)

> > > In order to make my trick work. We need to assure dev_queue_xmit() and
> > > dev_hard_start_xmit() accept shared skbs. As Eric pointed, pktgen also
> > > need dev->netdev_ops->ndo_start_xmit() accept shared skbs. We need to
> > > fix every ndo_start_xmit() one by one, then dev_hard_start_xmit(), and
> > > when dev_queue_xmit() is also fixed, my trick can be added back.
> > > :)
> > 
> > I'm not sure pktgen is right - even if it's safe in its case, it seems
> > to break some older rules, and drivers should really own the things.
> > So it needs reviewing first.
> 
> The idea we always try to keep is that the caller is responsible for the
> fate of the skb it sent. The callee will do things like make a copy or
> clone if it needed to make changes or keep the skb. Same should be
> expected of a driver.

Well, I'm not sure we talk about the same thing. I mean e.g. the
comment above dev_queue_xmit(); the caller passes all control to the
callee here.

Cheers,
Jarek P.

> [1] Jarek - so you dont misunderstand this as an overture - it means
> Keep It Simple Silly (or the principle of dumb we talked about) ;->

OK, I can remember the seventies too ;-)
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