PROBLEM: udp not delivered on special socket receive buffer size

PROBLEM: udp not delivered on special socket receive buffer size

[Matthias Welk]

Hi,

I reported the following problem allready to the linux-kernel mailinglist, but 
did not receive any answer. I hope you are the right contacts for this.

The probles is, that I did not receive any udp packets (224 bytes), if the 
receive buffer size (SO_RCVBUF) of the socket is set to a value below 831 
(??) bytes.
Yes, you may ask why such a low value, but I have no influence on this, 
because it is set in the Java Media Framework internally.
You can check this behaviour with a small c-program too.

So my question is:

Is this a bug or are there any reasons for this magic 831 bytes barrier ?

Thanks, Matthias.
-- 
---------------------------------------------------------------
From: Matthias Welk                   office:  +49-30-3463-7272
      FHG Fokus                       mobile:  +49-179- 1144752
      Kaiserin-Augusta-Allee 31       fax   :  +49-30-3463-8672
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Re: PROBLEM: udp not delivered on special socket receive buffer size

[kuznet]

HelloQ

> The probles is, that I did not receive any udp packets (224 bytes), if the=
> =20
> receive buffer size (SO_RCVBUF) of the socket is set to a value below 831=20
> (??) bytes.

Apparently, 831 is not enough to allow to queue such buffer.

Tune value of "rx_copybreak" for ethernet to value sort of 1000.
It is module parameter for most of drivers.


> Yes, you may ask why such a low value, but I have no influence on this,=20
> because it is set in the Java Media Framework internally.

No doubts, this piece of software was not ever tested and contains
lots of another bugs, you will get nothing but persistnet pain in ass
if you are going to use it seriously.

Alexey

Re: PROBLEM: udp not delivered on special socket receive buffer size

[Matthias Welk]

On Wednesday 10 July 2002 10:56, kuznet@ms2.inr.ac.ru wrote:

>> The probles is, that I did not receive any udp packets (224 bytes), if the=
>> =20
>> receive buffer size (SO_RCVBUF) of the socket is set to a value below 
831=20
>> (??) bytes.
>
>Apparently, 831 is not enough to allow to queue such buffer.
>
>Tune value of "rx_copybreak" for ethernet to value sort of 1000.
>It is module parameter for most of drivers.
>

But shouldn't it not be working without tuning via kernel module parameters ?
And where is the relation between the "rx_copybreak" -value and the socket, I 
mean why is it working if I increase receive buffer size ?
And shouldn't the minimum size set to a minum working value ?

Thanks, Matthias.
-- 
---------------------------------------------------------------
From: Matthias Welk                   office:  +49-30-3463-7272
      FHG Fokus                       mobile:  +49-179- 1144752
      Kaiserin-Augusta-Allee 31       fax   :  +49-30-3463-8672
      10589 Berlin		      email : welk@fokus.fhg.de
----------------------------------------------------------------

Re: PROBLEM: udp not delivered on special socket receive buffer size

[David S. Miller]

   From: Matthias Welk <welk@fokus.gmd.de>
   Date: Wed, 10 Jul 2002 09:45:11 +0200

   So my question is:
   
   Is this a bug or are there any reasons for this magic 831 bytes
   barrier ?

Assuming anything about the meaning of the send/receive buffer sizes,
as raw numbers, is going to cause no ends of problems for any
application.

Under Linux, the size of the socket buffer structure itself (not just
the data) is subtracted from the socket buffer size when accounting.
That is a perfectly legal thing to do.  So the Java code is broken.