linux-kernel - Re: [PATCH v2 0/5] Introduce DMA_HEAP_ALLOC_AND_READ

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Message-ID: <37b07e69-df85-45fc-888d-54cb7c4be97a@vivo.com>
Date: Tue, 30 Jul 2024 20:04:04 +0800
From: Huan Yang <link@...o.com>
To: Sumit Semwal <sumit.semwal@...aro.org>,
 Benjamin Gaignard <benjamin.gaignard@...labora.com>,
 Brian Starkey <Brian.Starkey@....com>, John Stultz <jstultz@...gle.com>,
 "T.J. Mercier" <tjmercier@...gle.com>,
 Christian König <christian.koenig@....com>,
 linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 linaro-mm-sig@...ts.linaro.org, linux-kernel@...r.kernel.org,
 opensource.kernel@...o.com
Subject: Re: [PATCH v2 0/5] Introduce DMA_HEAP_ALLOC_AND_READ_FILE heap flag

在 2024/7/30 17:05, Huan Yang 写道:
>
> 在 2024/7/30 16:56, Daniel Vetter 写道:
>> [????????? daniel.vetter@...ll.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