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Date:      Mon, 03 Dec 2001 14:22:06 -0800
From:      Terry Lambert <tlambert2@mindspring.com>
To:        Leo Bicknell <bicknell@ufp.org>
Cc:        Luigi Rizzo <rizzo@aciri.org>, freebsd-hackers@FreeBSD.ORG
Subject:   Re: TCP Performance Graphs
Message-ID:  <3C0BFB0E.829B39BC@mindspring.com>
References:  <20011130125839.A88302@ussenterprise.ufp.org> <20011130102928.E30981@iguana.aciri.org> <20011130141100.B90969@ussenterprise.ufp.org>

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Leo Bicknell wrote:
> 
> On Fri, Nov 30, 2001 at 10:29:28AM -0800, Luigi Rizzo wrote:
> > It is not a big deal to move the default to 32 or 64k, and I'd
> > vote for that, but if a sysadmin is unable to have a look at this,
> > then the problem is in the sysadmin, not in FreeBSD!
> 
> I disagree, on two points:
> 
> * Many people use FreeBSD as a desktop OS.  Think the same people
>   who use Win98, but only slightly smarter.  These people are
>   'sysadmins' only in the sense that they have a root password.
>   When FreeBSD can't fill their DSL line and Linux can, they will
>   switch to Linux never knowing what the real problem was.

It's not a good idea for very large servers, either.

When you doube the size, you quarter the maximum number of simultaneous
slow connections which you are able to have without overcommit (you
double both the input and output buffers for the sickets, meaning you
have 1/4 as many mbufs per socket available.

Normally, you overcommit, but, for example, if you were serving HTTP
content to multiple users on slow links from a FreeBSD box in a data
center, then the output buffers are commited after the first buffer
full, until all of the data has been sent.  For images, MP3's, etc.,
this means that the buffer is committed per connection for the remainder
of the connection until the data is completely transferred.

-- Terry

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