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[124.171.87.207]) by smtp.gmail.com with ESMTPSA id u44sm9699150pgn.81.2020.04.13.23.21.30 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 13 Apr 2020 23:21:33 -0700 (PDT) Subject: Re: [PATCH 1/2] dma-mapping: add a dma_ops_bypass flag to struct device From: Alexey Kardashevskiy 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> <95395244-bdec-84d2-b81b-3040c076fe4d@ozlabs.ru> Autocrypt: addr=aik@ozlabs.ru; keydata= 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Kardashevskiy wrote: > > > 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. Any plans on posting v3 of this? Thanks, > >> 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