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=-8.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 06C4EC43461 for ; Thu, 17 Sep 2020 10:39:52 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (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 75EA52087D for ; Thu, 17 Sep 2020 10:39:51 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="Slgis8Kj" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 75EA52087D Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Type: Content-Transfer-Encoding:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date:Message-ID:From: References:To:Subject:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=lwvd2tkZgfYG0rkUXSA6rBp6WEn1QdsFguUHMYtAKb4=; b=Slgis8Kjt91xo9MPEKVwQHXoC aE8l1FnNqv4FiCP1b0t3bfu8iRMvdbmtk1BTemgCRl99CU7Ba6wwsryjAjVaVAnuTYJE25tjLyr/O H2R1H45CZ/kv1/IdXCnWVFXcSwS05eILEgVkETp/fc6zg882eHFDveUlE7e2Tf4n+StOGuIm7zRkP oONPvkxKnKLSq4hYRMdk8XbyBwPOBmubaKZpoKxDAbf9u2A6nEu8y/PKkI0dRAwDmq6IyIfDo1StF snRaioHG1Fan/N+6cl5Gr/1D+P0v11E9KhqRy5gx81LpIIQsi6HNver6Vy7/OqX8fZK0Hct/515qY la969ZQFA==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kIrJI-0008W5-07; Thu, 17 Sep 2020 10:38:40 +0000 Received: from foss.arm.com ([217.140.110.172]) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kIrJE-0008V2-8n; Thu, 17 Sep 2020 10:38:37 +0000 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 ED87B30E; Thu, 17 Sep 2020 03:38:34 -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 995B73F68F; Thu, 17 Sep 2020 03:38:32 -0700 (PDT) Subject: Re: [PATCH 0/3] drm: panfrost: Coherency support To: Rob Herring , Alyssa Rosenzweig References: <20200916170409.GA2543@kevin> From: Steven Price Message-ID: Date: Thu, 17 Sep 2020 11:38:31 +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: Content-Language: en-GB X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200917_063836_377988_3656C49E X-CRM114-Status: GOOD ( 16.51 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Tomeu Vizoso , Neil Armstrong , Robin Murphy , dri-devel , Linux IOMMU , Kevin Hilman , "open list:ARM/Amlogic Meson..." , Will Deacon , linux-arm-kernel , Jerome Brunet Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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. Steve _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel