Re: [PATCH v5] net: ethernet: add driver for Aurora VLSI NB8800 Ethernet controller

From: Eric Dumazet <eric.dumazet@gmail.com>
To: "Måns Rullgård" <mans@mansr.com>
Cc: David Miller <davem@davemloft.net>,
	romieu@fr.zoreil.com, linux-kernel@vger.kernel.org,
	netdev@vger.kernel.org, slash.tmp@free.fr
Subject: Re: [PATCH v5] net: ethernet: add driver for Aurora VLSI NB8800 Ethernet controller
Date: Wed, 11 Nov 2015 06:09:21 -0800	[thread overview]
Message-ID: <1447250961.17135.104.camel@edumazet-glaptop2.roam.corp.google.com> (raw)
In-Reply-To: <yw1x1tbwpry3.fsf@unicorn.mansr.com>

On Wed, 2015-11-11 at 13:48 +0000, Måns Rullgård wrote:
> Eric Dumazet <eric.dumazet@gmail.com> writes:
> 
> > On Wed, 2015-11-11 at 13:04 +0000, Måns Rullgård wrote:
> >
> >> I tried that, and throughput (as measured by iperf3) dropped by 2%.
> >> Maybe I did something wrong.
> >
> > What link speed have you used, what was the throughput you got,
> > and is the receiver using the same NIC ?
> 
> 1Gbps link, 640 Mbps TCP transmit throughput to a PC with Intel NIC.
> Why does it matter what NIC the receiver has?

Because at 1Gb line rate, you better get GRO properly implemented in the
receiver, so that TCP stack does not send one ACK every 2 MSS.

Send speed is also dependent on the number of ACK packets the sender has
to process.

This is why I suggested you use napi_gro_receive() in your driver.