netdev - Re: [PATCH net v2] tcp: Force updating pcount after skb

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Date:	Tue, 09 Jun 2015 10:59:13 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Martin KaFai Lau <kafai@...com>
Cc:	netdev <netdev@...r.kernel.org>, Kernel Team <kernel-team@...com>,
	Grant Zhang <gzhang@...tly.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Neal Cardwell <ncardwell@...gle.com>,
	Yuchung Cheng <ycheng@...gle.com>
Subject: Re: [PATCH net v2] tcp: Force updating pcount after skb_pull()
 during mtu probing

On Tue, 2015-06-09 at 10:45 -0700, Martin KaFai Lau wrote:
> On Tue, Jun 09, 2015 at 10:06:25AM -0700, Eric Dumazet wrote:
> > I've been working on this, but still can get the bug triggering in
> > tcp_fragment(), no matter what (Neal patch , yours, mine...)
> Can you describe the test case that can reproduce it?

This might not be easy : I used a 40Gb testbed and following.

Warning triggers in about 30 minutes, but this might be related to some
unrelated traffic.

echo 4 >/proc/sys/net/ipv4/tcp_min_tso_segs
echo 0 >/proc/sys/kernel/timer_migration
echo fq >/proc/sys/net/core/default_qdisc
tc qd replace dev eth1 root mq
./super_netperf 1500 --google-pacing-rate 3028000 -H lpaa24 -l 10000 &

You might implement the pacing stuff using regular netperf with

for ETH in eth1
do
 tc qd del dev $ETH root 2>/dev/null
 tc qd add dev $ETH root handle 1: mq
 for i in `seq 1 16`
 do
  slot=$( printf %x $(( i )) )
  tc qd add dev $ETH parent 1:$slot fq maxrate 3028000
 done
done


(Change eth1 by eth0 or something, and 16 by number of TX queues.)


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