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Re: many outgoing tcp sockets are slower than a few

To: Lennert Buytenhek <buytenh@xxxxxxxxxxxxxx>
Subject: Re: many outgoing tcp sockets are slower than a few
From: Christian Schmid <webmaster@xxxxxxxxxxxxxx>
Date: Mon, 21 Feb 2005 20:11:30 +0100
Cc: bert hubert <ahu@xxxxxxx>, Nivedita Singhvi <niv@xxxxxxxxxx>, netdev@xxxxxxxxxxx
In-reply-to: <20050221172943.GA31814@xi.wantstofly.org>
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Lennert Buytenhek wrote:
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.


'syswrite'.

Is your application written in C or perl?


Perl. But this is not the source because as stated in another mail, I tried with 6 processes when it slows down at 500 connections each and with 2 processes where it only starts to slowdown at 2000 processes each.

Chris

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