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Re: [PATCH] Too aggressive cwnd backoff

To: John Heffner <jheffner@xxxxxxx>
Subject: Re: [PATCH] Too aggressive cwnd backoff
From: Baruch Even <baruch@xxxxxxxxx>
Date: Fri, 08 Apr 2005 22:33:58 +0100
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>, shemminger@xxxxxxxx, netdev@xxxxxxxxxxx, werner@xxxxxxxxxxxxxxx
In-reply-to: <Pine.LNX.4.58.0504071435450.17545@dexter.psc.edu>
References: <20050407164146.GA6479@ev-en.org> <20050407101653.2cc68db1@dxpl.pdx.osdl.net> <42557895.8040004@ev-en.org> <20050407113121.31b71a94.davem@davemloft.net> <Pine.LNX.4.58.0504071435450.17545@dexter.psc.edu>
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John Heffner wrote:
This test looks correct to me.  (We never touched it.)  It is the bounding
parameter specified in rate halving.  If you actually get down that far,
then rate halving is getting confused, though.

In my tests with either NewReno at high-BDP network settings (300Kbit/s, 120ms delay, BDP = 3200 packets), we always go into this confused mode.

It will always upon a drop go to a point between the one-half and one-quarter of the original cwnd, but then, due to performance problems at that point the queue is filled and lots of packets are getting lost in bursts after I disabled throttling, with throttling it goes even below one quarter.

If I understand you correctly this check (that I changed) is correct and should not be changed but rather that the bug is elsewhere. I'll give it another look when I have some more time.

Baruch


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