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

Huan Yang
2024-07-30T09:05:19Z

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

> 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