From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751204AbcGFFF7 (ORCPT ); Wed, 6 Jul 2016 01:05:59 -0400 Received: from wtarreau.pck.nerim.net ([62.212.114.60]:37810 "EHLO 1wt.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750780AbcGFFF5 (ORCPT ); Wed, 6 Jul 2016 01:05:57 -0400 Date: Wed, 6 Jul 2016 07:04:31 +0200 From: Willy Tarreau To: Marcin Wojtas Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, netdev@vger.kernel.org, davem@davemloft.net, linux@arm.linux.org.uk, sebastian.hesselbarth@gmail.com, andrew@lunn.ch, jason@lakedaemon.net, thomas.petazzoni@free-electrons.com, gregory.clement@free-electrons.com, nadavh@marvell.com, alior@marvell.com, nitroshift@yahoo.com, jaz@semihalf.com, Dmitri Epshtein , stable@vger.kernel.org Subject: Re: [PATCH net] net: mvneta: set real interrupt per packet for tx_done Message-ID: <20160706050431.GA26348@1wt.eu> References: <1467771538-31811-1-git-send-email-mw@semihalf.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1467771538-31811-1-git-send-email-mw@semihalf.com> User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, On Wed, Jul 06, 2016 at 04:18:58AM +0200, Marcin Wojtas wrote: > From: Dmitri Epshtein > > Commit aebea2ba0f74 ("net: mvneta: fix Tx interrupt delay") intended to > set coalescing threshold to a value guaranteeing interrupt generation > per each sent packet, so that buffers can be released with no delay. > > In fact setting threshold to '1' was wrong, because it causes interrupt > every two packets. According to the documentation a reason behind it is > following - interrupt occurs once sent buffers counter reaches a value, > which is higher than one specified in MVNETA_TXQ_SIZE_REG(q). This > behavior was confirmed during tests. Also when testing the SoC working > as a NAS device, better performance was observed with int-per-packet, > as it strongly depends on the fact that all transmitted packets are > released immediately. > > This commit enables NETA controller work in interrupt per sent packet mode > by setting coalescing threshold to 0. We had a discussion about this in January 2015 and I thought I sent a patch to change it but I can't find it, so I think it was only proposed to some users for testing. I also remember that on more recent kernels by then (>=3.13) we observed a slightly better performance with this value set to zero. Acked-by: Willy Tarreau Willy