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Date:      Thu, 11 Oct 2001 18:16:14 -0700 (PDT)
From:      Archie Cobbs <archie@dellroad.org>
To:        Mike Tancsa <mike@sentex.net>
Cc:        rizzo@aciri.org, freebsd-net@FreeBSD.ORG
Subject:   Re: strange results with increased  net.inet.ip.intr_queue_maxlen
Message-ID:  <200110120116.f9C1GEv18196@arch20m.dellroad.org>
In-Reply-To: <5.1.0.14.0.20011011164834.0728c2e0@marble.sentex.ca> "from Mike Tancsa at Oct 11, 2001 04:50:42 pm"

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Mike Tancsa writes:
> > > net.inet.ip.intr_queue_maxlen from 50 to 100.  and there didnt seem to be
> > > any positive results in terms of lessening the rate of
> > > net.inet.ip.intr_queue_drops.
> >
> >This is consistent with the situation where packets are received
> >at a rate faster than they are being consumed. No matter how big
> >your queue is, it's going to fill up eventually and overflow, and
> >all you're doing by increasing the queue length is adding latency
> >to all of those packets that you do process.
> 
> Hi, thanks for the info.  But wont I still pay a price, presumably at the 
> application layer for any packets that are lost and retransmitted ?  Apart 
> 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 ?

If the forwarding path is maxed out, then it is the application layer's
responsibility to back off (think TCP).

Pinging is an excellent way to determine latency.

-Archie

__________________________________________________________________________
Archie Cobbs     *     Packet Design     *     http://www.packetdesign.com

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