netdev - Re: [PATCH net v2] net: sched: do not requeue a NULL skb

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Message-ID: <1460389951.6473.555.camel@edumazet-glaptop3.roam.corp.google.com>
Date:	Mon, 11 Apr 2016 08:52:31 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Lars Persson <lars.persson@...s.com>
Cc:	Lars Persson <larper@...s.com>, netdev@...r.kernel.org,
	jhs@...atatu.com, linux-kernel@...r.kernel.org,
	xiyou.wangcong@...il.com
Subject: Re: [PATCH net v2] net: sched: do not requeue a NULL skb

On Mon, 2016-04-11 at 17:17 +0200, Lars Persson wrote:
> 
> On 04/11/2016 04:22 PM, Eric Dumazet wrote:
> > On Mon, 2016-04-11 at 15:38 +0200, Lars Persson wrote:
> >
> >> I though it would be prudent because the queue can be non-empty even for
> >> the case of skb=NULL. So should it be there in this patch, another patch
> >> or not at all ?
> >
> > Then maybe change return code ?
> >
> > It seems strange that a validate_xmit_skb_list() failure stops the
> > __qdisc_run() loop but schedules another round.
> >
> >
> 
> It was suggested by Cong Wang to return 0 in order to stop the loop. Do 
> you guys agree that the loop should be stopped for such failures ? Then 
> I will put the schedule call inside the if as you proposed earlier.

What are the causes of validate_xmit_skb_list() failures ?

If gso segmentations fail because of memory pressure, better free more
skbs right now.

In any case, having a single test " if (skb)  " sounds better to me,
to have a fast path.

So your first patch was probably a better idea.

v2 has two tests instead of one.