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[124.171.87.207]) by smtp.gmail.com with ESMTPSA id w134sm13401066pfd.41.2020.04.07.03.12.51 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 07 Apr 2020 03:12:54 -0700 (PDT) Subject: Re: [PATCH 1/2] dma-mapping: add a dma_ops_bypass flag to struct device To: Christoph Hellwig Cc: "Aneesh Kumar K.V" , iommu@lists.linux-foundation.org, linuxppc-dev@lists.ozlabs.org, Lu Baolu , Greg Kroah-Hartman , Joerg Roedel , Robin Murphy , linux-kernel@vger.kernel.org, Michael Ellerman References: <87sghz2ibh.fsf@linux.ibm.com> <20200323172256.GB31269@lst.de> <20200324075402.GJ23447@lst.de> <41975da3-3a4a-fc3c-2b90-8d607cf220e6@ozlabs.ru> <20200325083740.GC21605@lst.de> <213b0c7d-f908-b4f4-466d-6240c3622cd6@ozlabs.ru> <20200406115016.GA10941@lst.de> <348046e7-7a38-62d6-4df0-e4a537b98926@ozlabs.ru> <20200406171706.GA3231@lst.de> From: Alexey Kardashevskiy Autocrypt: addr=aik@ozlabs.ru; keydata= mQINBE+rT0sBEADFEI2UtPRsLLvnRf+tI9nA8T91+jDK3NLkqV+2DKHkTGPP5qzDZpRSH6mD 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ikTJSxWUKmh7OP5mrqhwNe0ezgGiWxxvyNwThOHc5JvpzJLd32VDFilbxgu4Hhnf6LcgZJ2c Zd44XWqUu7FzVOYaSgIvTP0hNrBYm/E6M7yrLbs3JY74fGzPWGRbBUHTZXQEqQnZglXaVB5V ZhSFtHopZnBSCUSNDbB+QGy4B/E++Bb02IBTGl/JxmOwG+kZUnymsPvTtnNIeTLHxN/H/ae0 c7E5M+/NpslPCmYnDjs5qg0/3ihh6XuOGggZQOqrYPC3PnsNs3NxirwOkVPQgO6mXxpuifvJ DG9EMkK8IBXnLulqVk54kf7fE0jT/d8RTtJIA92GzsgdK2rpT1MBKKVffjRFGwN7nQVOzi4T XrB5p+6ML7Bd84xOEGsj/vdaXmz1esuH7BOZAGEZfLRCHJ0GVCSssg== Message-ID: <95395244-bdec-84d2-b81b-3040c076fe4d@ozlabs.ru> Date: Tue, 7 Apr 2020 20:12:49 +1000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20200406171706.GA3231@lst.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/04/2020 03:17, Christoph Hellwig wrote: > On Mon, Apr 06, 2020 at 11:25:09PM +1000, Alexey Kardashevskiy wrote: >>>> Do you see any serious problem with this approach? Thanks! >>> >>> Do you have a link to the whole branch? The github UI is unfortunately >>> unusable for that (or I'm missing something). >> >> The UI shows the branch but since I rebased and forcepushed it, it does >> not. Here is the current one with: >> >> https://github.com/aik/linux/commits/dma-bypass.3 > > Ok, so we use the core bypass without persistent memory, and then > have another bypass mode on top. Not great, but I can't think > of anything better. Note that your checks for the map_sg case > aren't very efficient - for one it would make sense to calculate > the limit only once, Good points, I'll post revised version when you post your v3 of this. > but also it would make sense to reuse the > calculted diecect mapping addresses instead of doing another pass > later on in the dma-direct code. Probably but I wonder what kind of hardware we need to see the difference. I might try, just need to ride to the office to plug the cable in my 100GBit eth machines :) Thanks, -- Alexey