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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 52E0DC282CE for ; Wed, 22 May 2019 13:25:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2FCDD217F9 for ; Wed, 22 May 2019 13:25:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729755AbfEVNZr (ORCPT ); Wed, 22 May 2019 09:25:47 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:51378 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729126AbfEVNZq (ORCPT ); Wed, 22 May 2019 09:25:46 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 26F9615AB; Wed, 22 May 2019 06:25:46 -0700 (PDT) Received: from [10.1.26.184] (unknown [10.1.26.184]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id DA7E43F73F; Wed, 22 May 2019 06:25:44 -0700 (PDT) Subject: Re: [PATCH] swiotlb: sync buffer when mapping FROM_DEVICE To: Christoph Hellwig Cc: =?UTF-8?Q?Horia_Geant=c4=83?= , Konrad Rzeszutek Wilk , Marek Szyprowski , iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, linux-imx@nxp.com References: <20190522072018.10660-1-horia.geanta@nxp.com> <20190522123243.GA26390@lst.de> <6cbe5470-16a6-17e9-337d-6ba18b16b6e8@arm.com> <20190522130921.GA26874@lst.de> From: Robin Murphy Message-ID: Date: Wed, 22 May 2019 14:25:38 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20190522130921.GA26874@lst.de> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2019-05-22 2:09 pm, Christoph Hellwig wrote: > On Wed, May 22, 2019 at 01:50:47PM +0100, Robin Murphy wrote: >> Would that work out any different from the existing DMA_ATTR_SKIP_CPU_SYNC? >> >> If drivers are prepared to handle this issue from their end, they can >> already do so for single mappings by using that attr along with explicit >> partial syncs via dma_sync_single(). For page/sg mappings we'd still have >> the problem of identifying what part of "partial" actually matters, and >> probably having to add some additional new sync operations to cope. > > Except that the same optimization we are tripping over here is also > present in dma_sync_* - dma_sync_*_to_device with DMA_FROM_DEVICE is a > no-op in swiotlb. Sure, but that should be irrelevant since the effective problem here is in the sync_*_for_cpu direction, and it's the unmap which nobbles the buffer. If the driver does this: dma_map_single(whole buffer); dma_unmap_single(whole buffer); then it could instead do this and be happy: dma_map_single(whole buffer, SKIP_CPU_SYNC); dma_sync_single_for_cpu(updated part of buffer); dma_unmap_single(whole buffer, SKIP_CPU_SYNC); Robin. 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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 CAADCC282DD for ; Wed, 22 May 2019 13:25:48 +0000 (UTC) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org [140.211.169.12]) (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 A8C9221473 for ; Wed, 22 May 2019 13:25:48 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A8C9221473 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 mail.linux-foundation.org (localhost [127.0.0.1]) by mail.linuxfoundation.org (Postfix) with ESMTP id 5E901D83; Wed, 22 May 2019 13:25:48 +0000 (UTC) Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id A3A9DD7A for ; Wed, 22 May 2019 13:25:46 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from foss.arm.com (foss.arm.com [217.140.101.70]) by smtp1.linuxfoundation.org (Postfix) with ESMTP id 5DDBA883 for ; Wed, 22 May 2019 13:25:46 +0000 (UTC) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 26F9615AB; Wed, 22 May 2019 06:25:46 -0700 (PDT) Received: from [10.1.26.184] (unknown [10.1.26.184]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id DA7E43F73F; Wed, 22 May 2019 06:25:44 -0700 (PDT) Subject: Re: [PATCH] swiotlb: sync buffer when mapping FROM_DEVICE To: Christoph Hellwig References: <20190522072018.10660-1-horia.geanta@nxp.com> <20190522123243.GA26390@lst.de> <6cbe5470-16a6-17e9-337d-6ba18b16b6e8@arm.com> <20190522130921.GA26874@lst.de> From: Robin Murphy Message-ID: Date: Wed, 22 May 2019 14:25:38 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20190522130921.GA26874@lst.de> Content-Language: en-GB Cc: =?UTF-8?Q?Horia_Geant=c4=83?= , Konrad Rzeszutek Wilk , linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org, linux-imx@nxp.com X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.12 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" Sender: iommu-bounces@lists.linux-foundation.org Errors-To: iommu-bounces@lists.linux-foundation.org On 2019-05-22 2:09 pm, Christoph Hellwig wrote: > On Wed, May 22, 2019 at 01:50:47PM +0100, Robin Murphy wrote: >> Would that work out any different from the existing DMA_ATTR_SKIP_CPU_SYNC? >> >> If drivers are prepared to handle this issue from their end, they can >> already do so for single mappings by using that attr along with explicit >> partial syncs via dma_sync_single(). For page/sg mappings we'd still have >> the problem of identifying what part of "partial" actually matters, and >> probably having to add some additional new sync operations to cope. > > Except that the same optimization we are tripping over here is also > present in dma_sync_* - dma_sync_*_to_device with DMA_FROM_DEVICE is a > no-op in swiotlb. Sure, but that should be irrelevant since the effective problem here is in the sync_*_for_cpu direction, and it's the unmap which nobbles the buffer. If the driver does this: dma_map_single(whole buffer); dma_unmap_single(whole buffer); then it could instead do this and be happy: dma_map_single(whole buffer, SKIP_CPU_SYNC); dma_sync_single_for_cpu(updated part of buffer); dma_unmap_single(whole buffer, SKIP_CPU_SYNC); Robin. _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu