netdev - Re: [PATCH net] codel: fix maxpacket/mtu confusion

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Message-ID: <1430414369.3711.100.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Thu, 30 Apr 2015 10:19:29 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Dave Taht <dave.taht@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	Kathleen Nichols <nichols@...lere.com>,
	Van Jacobson <vanj@...gle.com>, netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net] codel: fix maxpacket/mtu confusion

On Thu, 2015-04-30 at 10:01 -0700, Dave Taht wrote:
> I long ago dropped the maxpacket check and the statistic/statistic
> collection from various test versions of codel in favor of either a
> constant (1500 byte) check or none at all. There is always some level
> of buffering underneath codel. I have always wanted the big
> GRO/TSO/GRO superpackets to get peeled apart also - the present system
> worked OK with ECN in most cases, but seemed  like it could get ugly
> if we started dropping 64k worth of superpacket.

The peeling part does not belong to codel or fq_codel, but eventually
the parent qdisc, like TBF (peeling is already there), or HTB (no
peeling yet)

codel has binary choice : drop or not drop.

Starting to doing X MSS drops out of GRO packets seems not needed to me
if sender is elastic (properly reacts to drop/ecn_marks). It put extra
logic in the wrong place.

Again, if you have GRO super packets in codel/fq_codel, it means the
sender is buggy enough to send big bursts. Just drop the big GRO packet,
do not try to be gentle with the bad guy.



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