Re: [PATCH v2 0/5] Introduce DMA_HEAP_ALLOC_AND_READ_FILE heap flag

Huan Yang
2024-07-30T12:04:12Z

在 2024/7/30 17:05, Huan Yang 写道:
>
> 在 2024/7/30 16:56, Daniel Vetter 写道:
>> [????????? daniel.vetter@ffwll.ch ?????????
>> https://aka.ms/LearnAboutSenderIdentification?????????????]
>>
>> On Tue, Jul 30, 2024 at 03:57:44PM +0800, Huan Yang wrote:
>>> UDMA-BUF step:
>>>    1. memfd_create
>>>    2. open file(buffer/direct)
>>>    3. udmabuf create
>>>    4. mmap memfd
>>>    5. read file into memfd vaddr
>> Yeah this is really slow and the worst way to do it. You absolutely want
>> to start _all_ the io before you start creating the dma-buf, ideally
>> with
>> everything running in parallel. But just starting the direct I/O with
>> async and then creating the umdabuf should be a lot faster and avoid
> That's greate,  Let me rephrase that, and please correct me if I'm wrong.
>
> UDMA-BUF step:
>   1. memfd_create
>   2. mmap memfd
>   3. open file(buffer/direct)
>   4. start thread to async read
>   3. udmabuf create
>
> With this, can improve

I just test with it. Step is:

UDMA-BUF step:
1. memfd_create
2. mmap memfd
3. open file(buffer/direct)
4. start thread to async read
5. udmabuf create

6 . join wait

3G file read all step cost 1,527,103,431ns, it's greate.

>
>> needlessly serialization operations.
>>
>> The other issue is that the mmap has some overhead, but might not be too
>> bad.
> Yes, the time spent on page fault in mmap should be negligible
> compared to the time spent on file read.
>> -Sima
>> --
>> Daniel Vetter
>> Software Engineer, Intel Corporation
>> http://blog.ffwll.ch