netdev - Re: HTB, HFSC, PIE, FIFO stuck on 2.4Gbit on default values

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Date:	Tue, 03 Nov 2015 14:02:22 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Andrew <nitr0@...i.kr.ua>
Cc:	Netdev <netdev@...r.kernel.org>
Subject: Re: HTB, HFSC, PIE, FIFO stuck on 2.4Gbit on default values

On Tue, 2015-11-03 at 23:04 +0200, Andrew wrote:
> Hi.
> 
> This is common trouble due to hierarchical shapers realization (global 
> tree lock on packet dequeuing - so when one CPU looks for parent class 
> where tokens can be borrowed, other CPUs are waiting). It's mentioned 
> even in academic publications :) You can read about it here: 
> http://www.ijcset.com/docs/IJCSET13-04-04-113.pdf
> 
> I think that simple lock removing will greatly improve performance; and 
> race conditions on packets dequeuing shouldn't hurt anything except 
> shaping accuracy. Another solutions looks more complex.

Thanks Andrew, I am very well aware of qdisc spinlock contention.

And race conditions on packets dequeueing will _crash_ your host.
Plainly.

This is why I am advising using GRO in the first place.


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