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Date:      Fri, 19 Oct 2001 21:19:54 -0400
From:      Mike Tancsa <mike@sentex.net>
To:        Marko Zec <zec@tel.fer.hr>
Cc:        freebsd-net@freebsd.org
Subject:   Re: fxp driver - receive interrupt bundling
Message-ID:  <5.1.0.14.0.20011019211817.05a05890@192.168.0.12>
In-Reply-To: <3BD0D063.C084B21D@tel.fer.hr>
References:  <SEN.1003532776.274194794@news.sentex.net> <o1i1ttcg3fbn3n8n4mlv64ta9kldnmskld@4ax.com>

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At 03:16 AM 10/20/2001 +0200, Marko Zec wrote:
>It doesn't matter how many fxp cards you have installed - if your box acts 
>as a
>server than most probably you can leave INT_DELAY at default value (Intel
>proposes 0x600, but I think 0x400 would be more appropriate).
>
>If you use your multi-fxp-card BSD box as a router, than the microcode will
>impose additional delay *twice* (once in each direction), so in that case the
>default value of 0x600 might be too high for achieving full 100 megE
>throughput, because of TCP windowing scheme having to wait for ACK frames,
>which will be held in fxp receive buffers too long. On the other hand, setting
>INT_DELAY too low minimizes the benefits of bundling interrupts, as fewer
>received frames get "bundled" on a single interrupt.
>
>To summarize: if you are doing any routing (or bridging as I do), find the 
>best
>value for INT_DELAY for your specific environment experimentally, it should be
>definitely smaller than or equal to 0x400. If you don't do packet forwarding
>between fxp interfaces, use the defaults.


Thanks!  This is for a router pushing upwards of 20Mb/s with about 110K 
routes on 4 interfaces. I will try and experiment a bit on my test setup 
first to see what works best.

         ---Mike
--------------------------------------------------------------------
Mike Tancsa,                          	          tel +1 519 651 3400
Sentex Communications,     			  mike@sentex.net
Providing Internet since 1994                    www.sentex.net
Cambridge, Ontario Canada			  www.sentex.net/mike


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