linux-kernel - Re: [PATCH 1/2] dma-mapping: add a dma_ops

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Message-ID: <44ad32a4-7ce5-4f4d-8237-53356f76f53a@ozlabs.ru>
Date:   Tue, 14 Apr 2020 16:21:27 +1000
From:   Alexey Kardashevskiy <aik@...abs.ru>
To:     Christoph Hellwig <hch@....de>
Cc:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        iommu@...ts.linux-foundation.org, linuxppc-dev@...ts.ozlabs.org,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Joerg Roedel <joro@...tes.org>,
        Robin Murphy <robin.murphy@....com>,
        linux-kernel@...r.kernel.org, Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH 1/2] dma-mapping: add a dma_ops_bypass flag to struct
 device



On 07/04/2020 20:12, Alexey 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