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

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Message-ID: <25cf34bd-b11f-4097-87b5-39e6b4a27d85@vivo.com>
Date: Tue, 30 Jul 2024 17:05:08 +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 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

> 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