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 8EE91C433EF for ; Tue, 31 May 2022 18:20:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242745AbiEaSUP (ORCPT ); Tue, 31 May 2022 14:20:15 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51202 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1346971AbiEaSTy (ORCPT ); Tue, 31 May 2022 14:19:54 -0400 Received: from linux.microsoft.com (linux.microsoft.com [13.77.154.182]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 228B39CC9C; Tue, 31 May 2022 11:19:52 -0700 (PDT) Received: from smtpclient.apple (d66-183-91-182.bchsia.telus.net [66.183.91.182]) by linux.microsoft.com (Postfix) with ESMTPSA id 7EECF20BE4FF; Tue, 31 May 2022 11:19:50 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 7EECF20BE4FF DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1654021191; bh=6tBRLXB2e8RGJAhBvRCWJggyD6cUh5gaL2NlANSFO3E=; h=Subject:From:In-Reply-To:Date:Cc:References:To:From; b=nnLnlFN18QpTmf2pxGdXKTd5CTRH+ISqH6g8Qx0KH4kWahuCrh9y6t6RO9R/vzWFH BjQ1ay5Vb/epIQW0KeVwjWHvTPZI97oyeDCRm0TRRWiDO4qlk9MdIQZfN5f/+tzfsl pScggM5IU9VolT+hDR97WnEeEPcKn+bpAt8jYoBo= Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3696.100.31\)) Subject: Re: [RFC 1/1] drivers/dma/*: replace tasklets with workqueue From: Allen Pais In-Reply-To: Date: Tue, 31 May 2022 11:19:49 -0700 Cc: Vinod Koul , Linus Walleij , Vincent Guittot , olivier.dautricourt@orolia.com, Stefan Roese , Kees Cook , linux-hardening@vger.kernel.org, Ludovic Desroches , Tudor Ambarus , Florian Fainelli , Ray Jui , Scott Branden , bcm-kernel-feedback-list , Nicolas Saenz Julienne , Paul Cercueil , Eugeniy.Paltsev@synopsys.com, Gustavo Pimentel , Viresh Kumar , Andy Shevchenko , Leo Li , zw@zh-kernel.org, Zhou Wang , Shawn Guo , Sascha Hauer , Sean Wang , Matthias Brugger , =?utf-8?Q?Andreas_F=C3=A4rber?= , Manivannan Sadhasivam , Logan Gunthorpe , Sanjay R Mehta , Daniel Mack , Haojian Zhuang , Robert Jarzmik , Andy Gross , Bjorn Andersson , Krzysztof Kozlowski , green.wan@sifive.com, Orson Zhai , Baolin Wang , Lyra Zhang , Patrice CHOTARD , Chen-Yu Tsai , =?utf-8?Q?Jernej_=C5=A0krabec?= , Samuel Holland , dmaengine@vger.kernel.org, Linux Kernel Mailing List Content-Transfer-Encoding: quoted-printable Message-Id: <708F627F-0F7D-477F-BDF7-274424501DA0@linux.microsoft.com> References: <20220419211658.11403-1-apais@linux.microsoft.com> <20220419211658.11403-2-apais@linux.microsoft.com> <0A9EDEDC-9E6C-47F8-89C0-48DCDD3F9DE3@linux.microsoft.com> To: Arnd Bergmann X-Mailer: Apple Mail (2.3696.100.31) Precedence: bulk List-ID: X-Mailing-List: dmaengine@vger.kernel.org >=20 > [note: something is wrong with your email client, your previous reply = appears to > be in HTML] >=20 Sorry, fixed it. >>> That is a good idea, lot of drivers are waiting for completion which = can >>> be signalled from hardirq, this would also reduce the hops we have = and >>> help improve latency a bit. On the downside, some controllers = provide >>> error information, which would need to be dealt with. >>=20 >>=20 >> I am not an expert in dma subsystem, but by using completion from >> Hardirq context be a concern? Especially with latency. >=20 > I don't see how: to the task waiting for the completion, there should > be no difference, and for the irq handler sending it, it just avoids > a few cycles going into softirq context. Thanks for clarification.=20 If I have understood it correctly, your suggestion is to move the = current Callback mechanism out to dmaengine as a generic helper function And introduce completion in dma_async_tx_descriptor to handle what Tasklets currently do. Thanks. >=20 >>> Yes that would be a very reasonable mechanism, thanks for the >>> suggestions. >>=20 >> I have started working on the idea of global softirq. A RFC should = be ready >> For review soon. >=20 > Ok, thanks! >=20 > Arnd