netdev - Re: [PATCH net-next-2.6] net_sched: sch_sfq: add backlog info in sfq_dump_class

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Date:	Thu, 16 Dec 2010 12:03:04 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jarek Poplawski <jarkao2@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Patrick McHardy <kaber@...sh.net>
Subject: Re: [PATCH net-next-2.6] net_sched: sch_sfq: add backlog info in
 sfq_dump_class_stats()

Le jeudi 16 décembre 2010 à 08:16 +0000, Jarek Poplawski a écrit :
> On 2010-12-15 19:18, Eric Dumazet wrote:
> > We currently return for each active SFQ slot the number of packets in
> > queue. We can also give number of bytes accounted for these packets.
> > 
> > tc -s class show dev ifb0
> > 
> > Before patch :
> > 
> > class sfq 11:3d9 parent 11: 
> >  (dropped 0, overlimits 0 requeues 0) 
> >  backlog 0b 3p requeues 0 
> >  allot 1266 
> > 
> > After patch :
> > 
> > class sfq 11:3e4 parent 11: 
> >  (dropped 0, overlimits 0 requeues 0) 
> >  backlog 4380b 3p requeues 0 
> >  allot 1212 
> > 
> > 
> > Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
> > ---
> >  net/sched/sch_sfq.c |    7 ++++++-
> >  1 file changed, 6 insertions(+), 1 deletion(-)
> > 
> > diff --git a/net/sched/sch_sfq.c b/net/sched/sch_sfq.c
> > index 3cf478d..cb331de 100644
> > --- a/net/sched/sch_sfq.c
> > +++ b/net/sched/sch_sfq.c
> > @@ -548,8 +548,13 @@ static int sfq_dump_class_stats(struct Qdisc *sch, unsigned long cl,
> >  {
> >  	struct sfq_sched_data *q = qdisc_priv(sch);
> >  	sfq_index idx = q->ht[cl-1];
> > -	struct gnet_stats_queue qs = { .qlen = q->qs[idx].qlen };
> > +	struct sk_buff_head *list = &q->qs[idx];
> > +	struct gnet_stats_queue qs = { .qlen = list->qlen };
> >  	struct tc_sfq_xstats xstats = { .allot = q->allot[idx] };
> > +	struct sk_buff *skb;
> > +
> > +	skb_queue_walk(list, skb)
> > +		qs.backlog += qdisc_pkt_len(skb);
> 
> I don't think you can walk this list without the qdisc lock.

So after checks, I confirm qdisc lock is held at this point, patch is
valid.

tc_fill_tclass() calls gnet_stats_start_copy_compat() (and locks
qdisc_root_sleeping_lock()), before calling 
 cl_ops->dump_stats(q, cl, &d)

Thanks !


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