netdev - Re: [PATCH net-next 0/5] qed/qede: Tunnel hardware GRO support

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Date:	Wed, 22 Jun 2016 14:52:34 -0700
From:	Rick Jones <rick.jones2@....com>
To:	Yuval Mintz <Yuval.Mintz@...gic.com>,
	Alexander Duyck <alexander.duyck@...il.com>
Cc:	Manish Chopra <manish.chopra@...gic.com>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Ariel Elior <Ariel.Elior@...gic.com>,
	Tom Herbert <tom@...bertland.com>,
	Hannes Frederic Sowa <hannes@...hat.com>
Subject: Re: [PATCH net-next 0/5] qed/qede: Tunnel hardware GRO support

On 06/22/2016 11:22 AM, Yuval Mintz wrote:
> But seriously, this isn't really anything new but rather a step forward in
> the direction we've already taken - bnx2x/qede are already performing
> the same for non-encapsulated TCP.

Since you mention bnx2x...   I would argue that the NIC firmware on 
those NICs driven by bnx2x is doing it badly.  Not so much from a 
functional standpoint I suppose, but from a performance one.  The 
NIC-firmware GRO done there has this rather unfortunate assumption about 
"all MSSes will be directly driven by my own physical MTU" and when it 
sees segments of a size other than would be suggested by the physical 
MTU, will coalesce only two segments together.  They then do not get 
further coalesced in the stack.

Suffice it to say this does not do well from a performance standpoint.

One can disable LRO via ethtool for these NICs, but what that does is 
disable old-school LRO, not GRO-in-the-NIC.  To get that disabled, one 
must also get the bnx2x module loaded with "disable-tpa=1" so the Linux 
stack GRO gets used instead.

Had the bnx2x-driven NICs' firmware not had that rather unfortunate 
assumption about MSSes I probably would never have noticed.

happy benchmarking,

rick jones