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=-3.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 6AE1BC433E1 for ; Tue, 18 Aug 2020 08:39:25 +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 36E6E2067C for ; Tue, 18 Aug 2020 08:39:25 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="D8WVmtcb"; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="sChHbAxd" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 36E6E2067C Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org 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-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=gsan4E4xY1gCkxTJXRqDMmiNGlskP5SVW4jDwBbAtu4=; b=D8WVmtcbVkP+7Paan2MDcDK8c Tot42rIwF2U8/AgI/Qy6b5pI398rg6HNH3qzb4MYJg+C2HumoWZFe8YBESMoxU9agvsW4D+Alc50o 3n0z0O7hP94xm8j8nFwLqy6aMM57xZ/N3pXeGCj46xkfk/APeh9l0ZMjx8lOz0kmMyoOEgCtHyNTs ccxfqTNbEbRlTGSmFCXVHztON+uF204did3yVVDINYGp/7j0aFWo4OFWA+4k2VPzxJgSUdX78LDht CtLdL/DNoRYQwxvrZeLhbfDgi1GdP4BI/QWS9XCJcbI7Emc90oLmmpc1YhmjK1hrnhWVWc9A0PfTq IrX+2l2aw==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1k7x7V-0006zv-3E; Tue, 18 Aug 2020 08:37:25 +0000 Received: from casper.infradead.org ([2001:8b0:10b:1236::1]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1k7x7S-0006zX-OO for linux-arm-kernel@merlin.infradead.org; Tue, 18 Aug 2020 08:37:22 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=z+RycezjV2WVCujs2S8itL6PhqDnVUaq7qp6xVdLAo4=; b=sChHbAxde70X2xuGN/HW+28KHz HI6YetzZL7SCINwQdD5+hHwkS6qWOP4voGDc8BYsONfhYhnkoQjB8JI7DJJ9WQFCYfhWEbCSaLAB/ omXVKQnx1SSatRgDqyYjcqU0OpvgaD2swot7bjhdFztT6gzNDrjEARqivLy9gDHU+rpvRWfZnA8TU EXesWd61vo9k2yjd6ObDCJVrP1fhwDN5MYWt/fXfGTXqq8r+QJLiuZzA0MqYq9MFwmi9U6wOVFmOZ 0288DMbrkGzzFf92AljB7ECFX3C4q0e5AVJDUpv6hEAlOSfHWemTogfSP8tf0Sw1RswoQai5g6knN CYOJR6QQ==; Received: from hch by casper.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1k7x7Q-0002kj-2n; Tue, 18 Aug 2020 08:37:20 +0000 Date: Tue, 18 Aug 2020 09:37:20 +0100 From: Christoph Hellwig To: Will Deacon Subject: Re: [PATCH 1/2] dma-mapping: introduce relaxed version of dma sync Message-ID: <20200818083720.GA9451@infradead.org> References: <1597736591-20457-1-git-send-email-pullip.cho@samsung.com> <20200818082852.GA15145@willie-the-truck> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200818082852.GA15145@willie-the-truck> X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.infradead.org. See http://www.infradead.org/rpr.html 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: janghyuck.kim@samsung.com, catalin.marinas@arm.com, joro@8bytes.org, linux-kernel@vger.kernel.org, hyesoo.yu@samsung.com, iommu@lists.linux-foundation.org, Cho KyongHo , robin.murphy@arm.com, linux-arm-kernel@lists.infradead.org, m.szyprowski@samsung.com Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Aug 18, 2020 at 09:28:53AM +0100, Will Deacon wrote: > On Tue, Aug 18, 2020 at 04:43:10PM +0900, Cho KyongHo wrote: > > Cache maintenance operations in the most of CPU architectures needs > > memory barrier after the cache maintenance for the DMAs to view the > > region of the memory correctly. The problem is that memory barrier is > > very expensive and dma_[un]map_sg() and dma_sync_sg_for_{device|cpu}() > > involves the memory barrier per every single cache sg entry. In some > > CPU micro-architecture, a single memory barrier consumes more time than > > cache clean on 4KiB. It becomes more serious if the number of CPU cores > > are larger. > > Have you got higher-level performance data for this change? It's more likely > that the DSB is what actually forces the prior cache maintenance to > complete, so it's important to look at the bigger picture, not just the > apparent relative cost of these instructions. > > Also, it's a miracle that non-coherent DMA even works, so I'm not sure > that we should be complicating the implementation like this to try to > make it "fast". And without not just an important in-tree user but one that actually matters and can show how this is correct the whole proposal is complete nonstarter. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel