From owner-freebsd-net  Thu Oct 11 18:33:47 2001
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From: Luigi Rizzo <rizzo@aciri.org>
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Subject: Re: strange results with increased  net.inet.ip.intr_queue_maxlen
In-Reply-To: <200110120116.f9C1GEv18196@arch20m.dellroad.org> from Archie Cobbs at "Oct 11, 2001  6:16:14 pm"
To: archie@dellroad.org (Archie Cobbs)
Date: Thu, 11 Oct 2001 18:30:37 -0700 (PDT)
Cc: mike@sentex.net, rizzo@aciri.org, freebsd-net@FreeBSD.ORG
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> > from pinging the other side of the OC-3 or ethernet connection and 
> > measuring the response time, how can I see how much latency is added by 
> > increasing these buffers ?

of course the latency increase depends on how full are the buffers,
and the worst case is easier to determine by back-of-the-envelope
calculations:

	queue_slots * max_pkt_size / bottleneck_link_speed

e.g. if you have 100 slots and an MSS of 1500 and a 10Mbit
bottleneck you are adding (100*1500*8 / 10000000) = 120ms latency.

	cheers
	luigi


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