netdev - Re: htb parallelism on multi-core platforms

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Date:	Wed, 29 Apr 2009 14:23:12 +0200
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Radu Rendec <radu.rendec@...s.ro>
Cc:	Jesper Dangaard Brouer <hawk@...u.dk>,
	Denys Fedoryschenko <denys@...p.net.lb>,
	netdev <netdev@...r.kernel.org>,
	Calin Velea <calin.velea@...enii.ro>
Subject: Re: htb parallelism on multi-core platforms

On Wed, Apr 29, 2009 at 02:03:26PM +0300, Radu Rendec wrote:
> On Wed, 2009-04-29 at 12:31 +0200, Jesper Dangaard Brouer wrote:
...
> > Yes, it looks like the problem is your u32 classification setup... Perhaps 
> > its not doing what you think its doing...  didn't Jarek provide some hints 
> > for you to follow?
> 
> I've just realized that I might be hitting the worst-case bucket with
> the (ip) destinations I chose for the test traffic. I'll try 
> 
> I haven't tried tweaking htb_hysteresis yet (that was one of Jarek's
> hints) - it's debatable that it would help since the real problem seems
> to be in u32 (not htb), but I'll give it a try anyway.

According to the author's(?) comment with hysteresis "The speed gain
is about 1/6", so not very much here considering htb_dequeue time.

> Another hint was to make sure that "tc class add" goes before
> corresponding "tc filter add" - checked: it's ok.
> 
> Another interesting hint came from Calin Velea, whose tests suggest that
> the overall performance is better with napi turned off, since (rx)
> interrupt work is distributed to all cpus/cores. I'll try to replicate
> this as soon as I make some small changes to my test setup so that I'm
> able to measure overall htb throughput on the egress nic (bps and pps).

Radu, since not only your worst case, but also the real case u32
lookups are very big I think you should mainly have a look at Calin's
u32 hash generator or at least his method, and only after optimizing
it try these other tricks. Btw. I hope Calin made this nice program
known to networking/admins lists too.

Btw. #2: I think you wrote you didn't use iptables...

Cheers,
Jarek P.
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