netdev - Re: many sockets, slow sendto

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Message-Id: <20070319.161611.70218081.davem@davemloft.net>
Date:	Mon, 19 Mar 2007 16:16:11 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	zacco@...hu
Cc:	baruch@...en.org, netdev@...r.kernel.org
Subject: Re: many sockets, slow sendto

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.

UDP apps can and do bind to specific destination addresses and
ports, but the source side is usually wild-carded.

Are both the source address and port fully specified for your
sockets?  Maybe we can do something using if that's the case...
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