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Re: many outgoing tcp sockets are slower than a few

To: Christian Schmid <webmaster@xxxxxxxxxxxxxx>
Subject: Re: many outgoing tcp sockets are slower than a few
From: Lennert Buytenhek <buytenh@xxxxxxxxxxxxxx>
Date: Mon, 21 Feb 2005 18:29:43 +0100
Cc: bert hubert <ahu@xxxxxxx>, Nivedita Singhvi <niv@xxxxxxxxxx>, netdev@xxxxxxxxxxx
In-reply-to: <421A179C.1030505@xxxxxxxxxxxxxx>
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On Mon, Feb 21, 2005 at 06:17:16PM +0100, Christian Schmid wrote:

> >>Outgoing data. I am using sendfile() to send the file on a non-blocking 
> >>socket but the call blocks for 100 ms per socket if I get over 3000 
> >>sockets. Thats causing the massive slowdown in sum. I first thought its a 
> >>disk-issue but I tried with pure-cache data as well and it still blocks.
> >
> >O_NONBLOCK send() is really nonblocking, but O_NONBLOCK sendfile()
> >really isn't, as it still does the disk read (if any) synchronously.
> >
> >How are you making sure that you're sending "pure-cache data"?
> Because thats the first I excluded. I changed the program by replacing 
> sendfile with a caching-routine plus syswrite. And it was really 
> interesting that the syswrite was the one which needs most of the 
> real-time, not the caching-routine. syswrite blocked 100 ms per socket.


Is your application written in C or perl?


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