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 X-Spam-Level: X-Spam-Status: No, score=-8.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B4FE7C433E0 for ; Tue, 9 Mar 2021 12:46:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6BA546525F for ; Tue, 9 Mar 2021 12:46:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229799AbhCIMqK (ORCPT ); Tue, 9 Mar 2021 07:46:10 -0500 Received: from mail-yb1-f170.google.com ([209.85.219.170]:40655 "EHLO mail-yb1-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229544AbhCIMqK (ORCPT ); Tue, 9 Mar 2021 07:46:10 -0500 Received: by mail-yb1-f170.google.com with SMTP id c131so13789665ybf.7 for ; Tue, 09 Mar 2021 04:46:09 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=iZVX4P6GO6TuP6ukYs5oXp8i0aZ0okK0rj5UnJMGUJk=; b=DhDBdejYugNkM5J8bGDTt2ZjPeOAijOF90zV9iuxmoLHp35rJG0Qyz19CUA7qV/zNt jk/JWG4V2hYRypiDovpawjmyBg+OKokfMXE+4JSQUQ8fMkCso6kySGm5VVr9KMhzKJgX NRkLSIedrCNolNNV6SBp9YbtsBQzGmCSruyBxakb5qnvm/w4X5WoFNPHkk0Lv5T5aoP7 FqW40b8OvWR+16uqzRrZgtatw0zs8IXViPxJ+PXKpYX+yLQVCM3v6Pz2WT2NFkrZ40TI IBEBJykOy6jAGiZOF9qYFC27g2TPWZs/96L+Z1J7PW77Yld8QTAaZM5xbZiMLCtFCZwf eXkw== X-Gm-Message-State: AOAM5305xFa+iC0Rbqzqum6Tctm20cqxmDzs47OQNJhSggwdRdcapxva oR9uHh184q4VzrfoDum/TtlmdbjdTFsRLI9CWAQ= X-Google-Smtp-Source: ABdhPJy8/qDhYu3gU+JR48ivgMQjBbZQrZ/gFyoNMXCJkth+72SVb6mOd0rtM8ir54uclHdDEH8W+7asJmM5dzzH0no= X-Received: by 2002:a25:254a:: with SMTP id l71mr39837035ybl.125.1615293969483; Tue, 09 Mar 2021 04:46:09 -0800 (PST) MIME-Version: 1.0 References: <20210308163445.103636-1-mailhol.vincent@wanadoo.fr> <20210308163445.103636-2-mailhol.vincent@wanadoo.fr> <2b43e72b-c561-d144-c01e-c4ea361cc932@pengutronix.de> In-Reply-To: <2b43e72b-c561-d144-c01e-c4ea361cc932@pengutronix.de> From: Vincent MAILHOL Date: Tue, 9 Mar 2021 21:45:58 +0900 Message-ID: Subject: Re: [PATCH v12 1/1] can: usb: etas_es58X: add support for ETAS ES58X CAN USB interfaces To: Marc Kleine-Budde Cc: linux-can , Arunachalam Santhanam Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-can@vger.kernel.org Hi Marc, On Tue. 9 Mar 2021 at 19:27, Marc Kleine-Budde wrote: > > On 3/8/21 5:34 PM, Vincent Mailhol wrote: > > This driver supports the ES581.4, ES582.1 and ES584.1 interfaces from > > ETAS GmbH (https://www.etas.com/en/products/es58x.php). > > > > Co-developed-by: Arunachalam Santhanam > > Signed-off-by: Arunachalam Santhanam > > Signed-off-by: Vincent Mailhol > > I'm not sure if you're supposed to change dql.min_limit from the driver. One thing for sure, I am the only one to do it. The reason to do so is because benchmarks show me that values below this threshold are not good for this device (and I try to be very permissive on the values). USB introduces a lot of latency and the small PDU of CAN does not help. The BQL is here to remediate, however, the algorithms can take time to adjust, especially if there are small bursts. Modifying the dql.min_limit was the only solution I found to make sure that packets can be sent in bulk even during small burst events. The BQL was not designed for USB nor was it designed for CAN which probably explains why I am the first one to ever have thought of using dql.min_limit like this. Using dql.min_limit is a hack and I pledge guilty for it. However, because this hack brings performance improvement, I would like to keep it if you do not mind. Yours sincerely, Vincent