From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id DF53AC433F5 for ; Tue, 10 May 2022 04:29:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236574AbiEJEc7 (ORCPT ); Tue, 10 May 2022 00:32:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50340 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236671AbiEJEbg (ORCPT ); Tue, 10 May 2022 00:31:36 -0400 Received: from metis.ext.pengutronix.de (metis.ext.pengutronix.de [IPv6:2001:67c:670:201:290:27ff:fe1d:cc33]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4FF174C422 for ; Mon, 9 May 2022 21:26:28 -0700 (PDT) Received: from ptx.hi.pengutronix.de ([2001:67c:670:100:1d::c0]) by metis.ext.pengutronix.de with esmtps (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1noHRr-00070V-Nc; Tue, 10 May 2022 06:26:11 +0200 Received: from ore by ptx.hi.pengutronix.de with local (Exim 4.92) (envelope-from ) id 1noHRp-0007KV-SV; Tue, 10 May 2022 06:26:09 +0200 Date: Tue, 10 May 2022 06:26:09 +0200 From: Oleksij Rempel To: Devid Antonio Filoni , Robin van der Gracht , kernel@pengutronix.de, linux-can@vger.kernel.org, Oleksij Rempel , Oliver Hartkopp , Marc Kleine-Budde , "David S. Miller" , Jakub Kicinski , Paolo Abeni , Maxime Jayat , kbuild test robot , netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH RESEND] can: j1939: do not wait 250ms if the same addr was already claimed Message-ID: <20220510042609.GA10669@pengutronix.de> References: <20220509170303.29370-1-devid.filoni@egluetechnologies.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: X-Sent-From: Pengutronix Hildesheim X-URL: http://www.pengutronix.de/ X-IRC: #ptxdist @freenode X-Accept-Language: de,en X-Accept-Content-Type: text/plain X-Uptime: 06:19:23 up 40 days, 16:49, 62 users, load average: 0.01, 0.09, 0.08 User-Agent: Mutt/1.10.1 (2018-07-13) X-SA-Exim-Connect-IP: 2001:67c:670:100:1d::c0 X-SA-Exim-Mail-From: ore@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: linux-can@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-can@vger.kernel.org Hi, On Mon, May 09, 2022 at 09:04:06PM +0200, Kurt Van Dijck wrote: > On ma, 09 mei 2022 19:03:03 +0200, Devid Antonio Filoni wrote: > > This is not explicitly stated in SAE J1939-21 and some tools used for > > ISO-11783 certification do not expect this wait. It will be interesting to know which certification tool do not expect it and what explanation is used if it fails? > IMHO, the current behaviour is not explicitely stated, but nor is the opposite. > And if I'm not mistaken, this introduces a 250msec delay. > > 1. If you want to avoid the 250msec gap, you should avoid to contest the same address. > > 2. It's a balance between predictability and flexibility, but if you try to accomplish both, > as your patch suggests, there is slight time-window until the current owner responds, > in which it may be confusing which node has the address. It depends on how much history > you have collected on the bus. > > I'm sure that this problem decreases with increasing processing power on the nodes, > but bigger internal queues also increase this window. > > It would certainly help if you describe how the current implementation fails. > > Would decreasing the dead time to 50msec help in such case. > > Kind regards, > Kurt > -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |