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From: Andy Furniss <andy.furniss@dsl.pipex.com>
To: lartc@vger.kernel.org
Subject: Re: [LARTC] HTB on loopback gives a bit rate multiplied by 8
Date: Thu, 02 Jun 2005 19:32:25 +0000	[thread overview]
Message-ID: <429F5EC9.5020202@dsl.pipex.com> (raw)
In-Reply-To: <5ee6fe61050601123763b42b29@mail.gmail.com>

Kiruthika Selvamani wrote:
> Hi Andy,
> Thanks for the suggestion. I changed the MTU to 1500 and it started
> working. Is this because HTB shapes traffic based on packet rate
> rather than bit rate? How does it use the rate lookup tables?

It's not based on packet rate as such, the lookup tables are for the 
time delay for different packet lengths at the different rates. There is 
one for each rate and ceil pre calculated for efficiency.

Each table has 256 slots so the mtu is needed to fill it efficiently, 
with normal mtu each slot is 8 bytes apart. If you had told htb the mtu 
of lo (16436) then each slot would have been calculated to cover a 
bigger range of bytes.

I suppose the giants counter is a warning that these packets are not 
being shaped properly as they are too big. I suppose devik decided to do 
this in preference to calculating the delay for every giant so it didn't 
slow things down too much.

Personally I am glad he didn't just use the interface mtu, as my dsl 
ppp0 gets one of 32k - it never sees a packet bigger than 1500 though, 
so if htb used 32k the shaping of small packets would be too innacurate.

Andy.

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      parent reply	other threads:[~2005-06-02 19:32 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2005-06-01 19:37 [LARTC] HTB on loopback gives a bit rate multiplied by 8 Kiruthika Selvamani
2005-06-01 21:28 ` Andy Furniss
2005-06-02 13:40 ` Kiruthika Selvamani
2005-06-02 19:32 ` Andy Furniss [this message]

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