Re: [PATCH 1/2] dma-mapping: add a dma_ops_bypass flag to struct device

[Alexey Kardashevskiy]

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