From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joao Pinto Subject: Re: [PATCH v2 net-next] net: stmmac: add drop transmit status feature Date: Wed, 12 Apr 2017 14:16:13 +0100 Message-ID: <37cc8294-5514-ed02-9b41-86f8cc9c20ad@synopsys.com> References: <20170412115643.GA32596@lunn.ch> <20170412131008.GC32596@lunn.ch> Mime-Version: 1.0 Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 8bit Cc: , To: Andrew Lunn , Joao Pinto Return-path: Received: from us01smtprelay-2.synopsys.com ([198.182.60.111]:39402 "EHLO smtprelay.synopsys.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751816AbdDLNQS (ORCPT ); Wed, 12 Apr 2017 09:16:18 -0400 In-Reply-To: <20170412131008.GC32596@lunn.ch> Sender: netdev-owner@vger.kernel.org List-ID: Ās 2:10 PM de 4/12/2017, Andrew Lunn escreveu: >>>> +- snps,drop-tx-status: this enables drop tx status >>> >>> Hi Joao >>> >>> Was the conclusion from testing that this cannot be turned on by >>> default? >> >> This feature is great for applications that need good performance, but has a >> drawback since it has an impact in timestamp feature in Tx. There are some >> operations in PTP where the timestamp is given to the host through the TX status >> in the descriptor, so this will have an impact. >> >> There's a way of solving this of course by making the driver checking the >> timestamp in the MAC_Tx_Timestamp_Status_XXX registers, but I can only look into >> that feature later in the future. > > The problem you have is that the device tree binding is a Binary API > you have to keep backwards compatible with for the next 20 years. You > cannot drop this property when you do get around to finishing the > work. You also want to avoid adding more and more options, which > nobody knows what they do, and what best combination is to get the > best performance. You should be aiming for a driver which just works > without any configuration and with good performance. > >>> What sort of performance improvement did you get? Do you have some >>> benchmark numbers? >> >> My setup is FPGA based, so it will have lower performance values. >> Iperf results with >> "Drop Transmit Status" set: ~650Mbps. >> "Drop Transmit Status" unset: ~450Mbps. > > What percentage of your customers use FPGAs? When i look at the users > of this driver, i see ST, Allwinner, Rockchip, Meson, etc. So silicon, > not FPGA. Does it make sense to do performance measurements on FPGA, > when you say it has lower performance? I don't understand your question. Synopsys is an IP vendor, so all recent IPs are available for prototyping as you can understand and so early development is done using a FPGA. I only mentioned that the values were from a FPGA based setup because you could think that they were low. Performance values are just an indication. > > Andrew > Joao