Re: [Xen-devel] [PATCH] xen/arm: io: add function swap_mmio_handler()

[chenbaodong <chenbaodong@mxnavi.com>]

On 6/12/19 20:21, Julien Grall wrote:
> Hi,
>
> On 12/06/2019 11:08, chenbaodong wrote:
>>
>> On 6/12/19 17:08, Julien Grall wrote:
>>> Hi,
>>>
>>> On 6/12/19 6:42 AM, Baodong Chen wrote:
>>>> Swap function can be used when calling sort().
>>>> or else, the default swap function generic_swap() is used,
>>>> which is a little inefficient.
>>>
>>> I am not entirely convince this will be more efficient. mmio_handler 
>>> does not fit in 64 bit, so the compiler may decide to do either 
>>> multiple load or replace with a memcpy.
>>
>> Hello Julien,
>>
>> I have checked the disassemble result,
>>
>> and IIUC generic_swap has a loop so it should be a little 
>> inefficient. I'm not expert about hardware, please correct me if i'm 
>> wrong.
>
> I am not an hardware expert too... But as I pointed out below this is 
> a micro-optimization. In other words, you are tailoring a specific 
> function that may run faster now, but this is improvement is going to 
> be lost as this is just a very tiny part of the domain creation.
>
> [...]
>
>>>
>>> So at best this feels some micro-optimization. But then, this is 
>>> only call a limited number of time at each domain build. Is it 
>>> really worth it?
>>
>> It's not hot path here.
>>
>> Not sure about worth.
>>
>> Personally  i will try my best to do things well according to my 
>> understanding.
>
> Micro-optimization are always good, but you also have to factor the 
> cost of maintaining and whether this will improve significantly Xen.
>
>>
>>>
>>> On a side note, I have noticed you are sending a lot of 
>>> optimization/clean-up patch. What is your end goal here?
>>
>> My goal is to understand how xen works well.
>>
>>>
>>> If it is to improve the performance, then there are much bigger fish 
>>> to fry within Xen code base. I am happy to point some of them based 
>>> on where you are looking to improve.
>>
>> Surly i want to improve performance.
>>
>> Features like Fast Startup ( I learned from xen summit 2018, samsung 
>> automotive presentation).
>>
>> But currently i don't understand xen well, only a few weeks experience.
>
> We do have small task for newcomers that would improve Xen code base 
> and also allow your to understand more some part of the code.
>
> If you have a specific area of interest, I can see if I have some 
> small tasks there.

I'm happy with this.

Interested in arm platform for embedded and automotive use case.

things like in this link: 
https://xenproject.org/developers/teams/embedded-and-automotive/


>
> Cheers,
>

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