netdev - Re: kernel panic in 4.2.3, rb_erase in sch

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Date:	Mon, 02 Nov 2015 17:58:11 +0200
From:	Denys Fedoryshchenko <nuclearcat@...learcat.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Jamal Hadi Salim <jhs@...atatu.com>,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: kernel panic in 4.2.3, rb_erase in sch_fq

On 2015-11-02 17:24, Eric Dumazet wrote:
> On Mon, 2015-11-02 at 16:11 +0200, Denys Fedoryshchenko wrote:
>> Hi!
>> 
>> Actually seems i was getting this panic for a while (once per week) on
>> loaded pppoe server, but just now was able to get full panic message.
>> After checking commit logs on sch_fq.c i didnt seen any fixes, so
>> probably upgrading to newer kernel wont help?
> 
> I do not think we support sch_fq as a HTB leaf.
> 
> If you want both HTB and sch_fq, you need to setup a bonding device.
> 
> HTB on bond0
> 
> sch_fq on the slaves
> 
> Sure, the kernel should not crash, but HTB+sch_fq on same net device is
> certainly not something that will work anyway.
Strange, because except ppp, on static devices it works really very well 
in such scheme. It is the only solution that can throttle incoming 
bandwidth, when bandwidth is very overbooked - reliably, for my use 
cases, such as 256k+ flows/2.5Gbps and several different classes of 
traffic, so using DRR will end up in just not enough classes.

On latest kernels i had to patch tc to provide parameter for orphan mask 
in fq, to increase number for flows for transit traffic.
None of other qdiscs able to solve this problem, incoming bandwidth 
simply flowing 10-20% more than set, but fq is doing magic.
The only device that was working with similar efficiency for such cases 
- proprietary PacketShaper, but is modifying tcp window size, and can't 
be called transparent, and also has stability issues over 1Gbps.
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