From: chenbaodong <chenbaodong@mxnavi.com>
To: Julien Grall <julien.grall@arm.com>, <xen-devel@lists.xenproject.org>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Subject: Re: [Xen-devel] [PATCH] xen/arm: io: add function swap_mmio_handler()
Date: Thu, 13 Jun 2019 08:31:27 +0800 [thread overview]
Message-ID: <36531850-15de-2642-6f28-c752a360959c@mxnavi.com> (raw)
In-Reply-To: <7c645dfb-72f5-5fc2-b559-0a4d09ba8801@arm.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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next prev parent reply other threads:[~2019-06-13 0:32 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-12 5:42 [Xen-devel] [PATCH] xen/arm: io: add function swap_mmio_handler() Baodong Chen
2019-06-12 9:08 ` Julien Grall
2019-06-12 10:08 ` chenbaodong
2019-06-12 12:21 ` Julien Grall
2019-06-13 0:31 ` chenbaodong [this message]
2019-06-24 18:18 ` Stefano Stabellini
2019-06-24 18:27 ` Stefano Stabellini
2019-06-24 19:27 ` Julien Grall
2019-06-24 20:17 ` Stefano Stabellini
2019-06-24 21:18 ` Julien Grall
2019-06-24 23:59 ` Stefano Stabellini
2019-06-25 8:46 ` Julien Grall
2019-06-27 23:30 ` chenbaodong
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