netdev - Re: many sockets, slow sendto

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <4600592E.80605@fw.hu>
Date:	Tue, 20 Mar 2007 22:59:10 +0100
From:	Zacco <zacco@...hu>
To:	David Miller <davem@...emloft.net>
CC:	baruch@...en.org, netdev@...r.kernel.org
Subject: Re: many sockets, slow sendto

Hi,

David Miller wrote:
> From: Zacco <zacco@...hu>
> Date: Tue, 20 Mar 2007 00:10:19 +0100
>
>   
>> As you recommended, I used oprofile and it turned out that the 
>> __udp4_lib_lookup function spent most of the time. There is a udp hash 
>> table and the sockets are sought based on the 7 LSBs of the destination 
>> port number. So what happened is now quite obvious: I had many thousands 
>> of sockets, all with the same destination port, thus linked in the same 
>> slot of this hash table. I tried using different ports and it
>> was much faster then.
>>     
>
> There isn't much we can do here.  I bet your destination address
> is unchanging just like your destination ports.
>   
As I'm simulating independent users on one host, each user has a 
different IP address, but each with the same port. So unlike the port, 
the address is changing, basically it's a huge A-class range.

> UDP apps can and do bind to specific destination addresses and
> ports, but the source side is usually wild-carded.
>   
Right, usually it is, but in my case the source addresses are also 
bound, otherwise the source address would be the primary address of the 
physical interface; however, I need to simulate users as if they were on 
separate hosts.
> Are both the source address and port fully specified for your
> sockets?  Maybe we can do something using if that's the case...
>   
You made me curious.  :)  What do you have in mind?

thx: Zacco
-
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html