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

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Date:	Wed, 11 Nov 2015 14:35:21 +0000
From:	Måns Rullgård <mans@...sr.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>, romieu@...zoreil.com,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	slash.tmp@...e.fr
Subject: Re: [PATCH v5] net: ethernet: add driver for Aurora VLSI NB8800 Ethernet controller

Måns Rullgård <mans@...sr.com> writes:

> Eric Dumazet <eric.dumazet@...il.com> writes:
>
>> On Wed, 2015-11-11 at 13:48 +0000, Måns Rullgård wrote:
>>> Eric Dumazet <eric.dumazet@...il.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.
>
> FWIW, with UDP I get 650 Mbps.

It seems the on-chip interconnect is limiting memory bandwidth available
to the Ethernet DMA.  If I increase the limits, I get 800 Mbps over TCP
and 850 Mbps over UDP with the driver posted here, the TCP case being
CPU bound in csum_partial_copy_from_user.

-- 
Måns Rullgård
mans@...sr.com
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