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Date:      Mon, 19 Nov 2001 00:58:06 -0800
From:      Luigi Rizzo <rizzo@aciri.org>
To:        Vladimir Girnetz <vg@ns.moldnet.md>
Cc:        net@FreeBSD.ORG
Subject:   Re: ipfw + pipes
Message-ID:  <20011119005806.A9378@iguana.aciri.org>
In-Reply-To: <20011119104807.D70300-100000@ns.moldnet.md>
References:  <20011119104807.D70300-100000@ns.moldnet.md>

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On Mon, Nov 19, 2001 at 10:49:11AM +0200, Vladimir Girnetz wrote:
> Hi
> 
> How many pipes can be created under FreeBSD 4.4?

as many as 64k independent pipes, each of which can have
a large number (default 1k, but can be soft-configurable) of
dynamic pipes. So essentially it is limited by the available RAM.

> How the number of pipes will be reflected on usage of CPU and RAM?

space is linear in the total number of pipes, per packet
processing time is in the worst case logarithmic in the number
of active pipes (i.e. those with backlogged traffic).
But basically, for most practical applications the performance
hit will go unnoticed, and even with the most complex configurations
I wouldn't expect a slowdown of more than a factor of 2.

[and i hear screams in the background from people who think
"oh no, for my application more than 1% overhead is unacceptable"
to whom i suggest to run "top" in a window, quickly move the mouse
around, and enjoy the "interrupt" stats going up...]

	cheers
	luigi
----------------------------------+-----------------------------------------
 Luigi RIZZO, luigi@iet.unipi.it  . ACIRI/ICSI (on leave from Univ. di Pisa)
 http://www.iet.unipi.it/~luigi/  . 1947 Center St, Berkeley CA 94704
 Phone: (510) 666 2927
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