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=-9.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 8BFDBC433DB for ; Thu, 18 Mar 2021 21:32:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 48F7264F11 for ; Thu, 18 Mar 2021 21:32:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230297AbhCRVbq (ORCPT ); Thu, 18 Mar 2021 17:31:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33974 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233192AbhCRVbU (ORCPT ); Thu, 18 Mar 2021 17:31:20 -0400 Received: from mail-pl1-x62d.google.com (mail-pl1-x62d.google.com [IPv6:2607:f8b0:4864:20::62d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4DDFDC06174A; Thu, 18 Mar 2021 14:31:20 -0700 (PDT) Received: by mail-pl1-x62d.google.com with SMTP id k4so1949967plk.5; Thu, 18 Mar 2021 14:31:20 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=urs31C1oCCeprVuwl2xS/PR4GaFAJl/+dTB9iEb63mU=; b=KZbC1ubJfdJSCMLlYSsz53FpXhle0Z79REbw0h4uYlS+NaKZD+4i06PhYx8XcW3OEm S24OKPOUpysAb9kFqBIh4omlHLsQ4K5+3GWlbW1LDCjNASBOzZbDcugMWxGt718SO2aF bvh+g72bGJSm89bwqurmoPeSF+7QMLcyvSE+otVFWljC2/jgyAzz5H8L6D1EMSA0BypU /q9TLEuSCO6ecJSoPnnq9IZfbVdHX8KWf6R+pP+i3oS5qjo0QtxTMQeeVVH19WYZ/Ml+ C+X7WLD3lMfI7KfY3yLzro7oLvlcWVCv2JDrk9EktIzaOwgXbeFibEbeuCDFJ43HWImo Drcw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=urs31C1oCCeprVuwl2xS/PR4GaFAJl/+dTB9iEb63mU=; b=P0jGeDYMfQ41p5xTNQylXcQRncmkhzmnWj4ITlNUQFQskXBrPznARnvoOwaIIGM5zv dLimhuwomVWcrVMSDWR3G9/c8neP+HNnbmjkUIb7gaUW28FWNTeKoCh7WIqoxu/IWOR+ gS3ghdGOsqbwd97kypu/C+jPztP5HA61sr1XWi2MnmPZQ/MwlH01/HEBnKGOp6wPXPKz kILAUBoED0iU5THCg4BTSGRwD/QCaRlqTu9ugZFjCPGcroTMeyefcDCj3T0n6ehPWJFT YgqpgQxoPV2uLxCGLvrSD6F5yq3FCBRXMc1R1PCbKmg5v57LPTWUh+aHc57F3O+yJzXm IQNw== X-Gm-Message-State: AOAM530ILfj43fvxB4DKmkacrLgWVfF7a5YSDr+K3+mBkry9ijWc/Pxk SMyrqtwQxRzAOvu4jqpXYt0= X-Google-Smtp-Source: ABdhPJwZynkHFeh94Ggvq5VKM7xZxZxokfdCvK0mYjOVVb3AS6xB6y2N36hJoyMG2e42huOSBG8I5g== X-Received: by 2002:a17:90a:bf04:: with SMTP id c4mr6268131pjs.170.1616103079707; Thu, 18 Mar 2021 14:31:19 -0700 (PDT) Received: from [10.230.29.202] ([192.19.223.252]) by smtp.gmail.com with ESMTPSA id j35sm3220312pgj.45.2021.03.18.14.31.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 18 Mar 2021 14:31:19 -0700 (PDT) Subject: Re: [PATCH] swiotlb: Add swiotlb=off to disable SWIOTLB To: Robin Murphy , linux-kernel@vger.kernel.org, Christoph Hellwig Cc: Jonathan Corbet , opendmb@gmail.com, "Paul E. McKenney" , Konrad Rzeszutek Wilk , Mauro Carvalho Chehab , Viresh Kumar , Randy Dunlap , "open list:DOCUMENTATION" , Peter Zijlstra , "open list:SWIOTLB SUBSYSTEM" , Andrew Morton , Mike Kravetz , Thomas Gleixner References: <20210318191816.4185226-1-f.fainelli@gmail.com> <16d1c66f-5451-2515-af73-a6b44d996e92@arm.com> From: Florian Fainelli Message-ID: Date: Thu, 18 Mar 2021 14:31:15 -0700 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Firefox/78.0 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: <16d1c66f-5451-2515-af73-a6b44d996e92@arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On 3/18/2021 12:53 PM, Robin Murphy wrote: > On 2021-03-18 19:43, Florian Fainelli wrote: >> >> >> On 3/18/2021 12:34 PM, Robin Murphy wrote: >>> On 2021-03-18 19:22, Florian Fainelli wrote: >>>> >>>> >>>> On 3/18/2021 12:18 PM, Florian Fainelli wrote: >>>>> It may be useful to disable the SWIOTLB completely for testing or >>>>> when a >>>>> platform is known not to have any DRAM addressing limitations what so >>>>> ever. >>> >>> Isn't that what "swiotlb=noforce" is for? If you're confident that we've >>> really ironed out *all* the awkward corners that used to blow up if >>> various internal bits were left uninitialised, then it would make sense >>> to just tweak the implementation of what we already have. >> >> swiotlb=noforce does prevent dma_direct_map_page() from resorting to the >> swiotlb, however what I am also after is reclaiming these 64MB of >> default SWIOTLB bounce buffering memory because my systems run with >> large amounts of reserved memory into ZONE_MOVABLE and everything in >> ZONE_NORMAL is precious at that point. > > It also forces io_tlb_nslabs to the minimum, so it should be claiming > considerably less than 64MB. IIRC the original proposal *did* skip > initialisation completely, but that turned up the aforementioned issues. AFAICT in that case we will have iotlb_n_slabs will set to 1, which will still make us allocate io_tlb_n_slabs << IO_TLB_SHIFT bytes in swiotlb_init(), which still gives us 64MB. > >>> I wouldn't necessarily disagree with adding "off" as an additional alias >>> for "noforce", though, since it does come across as a bit wacky for >>> general use. >>> >>>>> Signed-off-by: Florian Fainelli >>>> >>>> Christoph, in addition to this change, how would you feel if we >>>> qualified the swiotlb_init() in arch/arm/mm/init.c with a: >>>> >>>> >>>> if (memblock_end_of_DRAM() >= SZ_4G) >>>>      swiotlb_init(1) >>> >>> Modulo "swiotlb=force", of course ;) >> >> Indeed, we would need to handle that case as well. Does it sound >> reasonable to do that to you as well? > > I wouldn't like it done to me personally, but for arm64, observe what > mem_init() in arch/arm64/mm/init.c already does. > > Robin. -- Florian