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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 CF2FBC2BBD1 for ; Thu, 17 Sep 2020 11:01:07 +0000 (UTC) Received: from fraxinus.osuosl.org (smtp4.osuosl.org [140.211.166.137]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 46E1D2076D for ; Thu, 17 Sep 2020 11:01:07 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 46E1D2076D Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=iommu-bounces@lists.linux-foundation.org Received: from localhost (localhost [127.0.0.1]) by fraxinus.osuosl.org (Postfix) with ESMTP id ECEDD86FF2; Thu, 17 Sep 2020 11:01:06 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from fraxinus.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id VtWi1gVtGOda; Thu, 17 Sep 2020 11:01:06 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by fraxinus.osuosl.org (Postfix) with ESMTP id 4957D86FC4; Thu, 17 Sep 2020 11:01:06 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id 3F5E9C0864; Thu, 17 Sep 2020 11:01:06 +0000 (UTC) Received: from silver.osuosl.org (smtp3.osuosl.org [140.211.166.136]) by lists.linuxfoundation.org (Postfix) with ESMTP id EA34AC0051 for ; Thu, 17 Sep 2020 11:01:04 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by silver.osuosl.org (Postfix) with ESMTP id 857252E184 for ; Thu, 17 Sep 2020 11:01:04 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from silver.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id Io5VTAqUFNBg for ; Thu, 17 Sep 2020 11:01:03 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by silver.osuosl.org (Postfix) with ESMTP id 215412746F for ; Thu, 17 Sep 2020 11:01:02 +0000 (UTC) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 5E5E130E; Thu, 17 Sep 2020 04:01:02 -0700 (PDT) Received: from [192.168.1.79] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 4E8523F68F; Thu, 17 Sep 2020 04:01:00 -0700 (PDT) Subject: Re: [PATCH 0/3] drm: panfrost: Coherency support To: Tomeu Vizoso , Rob Herring , Alyssa Rosenzweig References: <20200916170409.GA2543@kevin> <0518e067-3b9a-8fe3-619f-8fce4c6c9677@collabora.com> From: Steven Price Message-ID: <51a06e78-7b80-c65d-67c4-e026e729e505@arm.com> Date: Thu, 17 Sep 2020 12:00:58 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <0518e067-3b9a-8fe3-619f-8fce4c6c9677@collabora.com> Content-Language: en-GB Cc: Neil Armstrong , Robin Murphy , dri-devel , Linux IOMMU , Kevin Hilman , "open list:ARM/Amlogic Meson..." , Will Deacon , linux-arm-kernel , Jerome Brunet X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On 17/09/2020 11:51, Tomeu Vizoso wrote: > On 9/17/20 12:38 PM, Steven Price wrote: >> On 16/09/2020 18:46, Rob Herring wrote: >>> On Wed, Sep 16, 2020 at 11:04 AM Alyssa Rosenzweig >>> wrote: >>>> >>>>> So I get a performance regression with the dma-coherent approach, >>>>> even if it's >>>>> clearly the cleaner. >>>> >>>> That's bizarre -- this should really be the faster of the two. >>> >>> Coherency may not be free. CortexA9 had something like 4x slower >>> memcpy if SMP was enabled as an example. I don't know if there's >>> anything going on like that specifically here. If there's never any >>> CPU accesses mixed in with kmscube, then there would be no benefit to >>> coherency. >> >> The DDK blob has the ability to mark only certain areas of memory as >> coherent for performance reasons. For simple things like kmscube I >> would expect that it's basically write-only from the CPU and almost >> all memory the GPU touches isn't touched by the CPU. I.e. coherency >> isn't helping and the coherency traffic is probably expensive. Whether >> the complexity is worth it for "real" content I don't know - it may >> just be silly benchmarks that benefit. > > Or maybe it's only a problem for applications that do silly things? I > don't think kmscube was ever optimized for performance. Well doing silly things is almost the definition of a benchmark ;) A lot of the mobile graphics benchmarks suffer from not being very intelligent in how they render (e.g. many have meshes that are far too detailed so the triangles are smaller than the pixels). Of course there are also applications that get things wrong too. Steve _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu