Am 30.07.24 um 11:05 schrieb Huan Yang:

在 2024/7/30 16:56, Daniel Vetter 写道:

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[????????? daniel.vetter@ffwll.ch ????????? https://aka.ms/LearnAboutSenderIdentification?????????????]

On Tue, Jul 30, 2024 at 03:57:44PM +0800, Huan Yang wrote:

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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

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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.

You should try to avoid mmap as much as possible. Especially the TLB invalidation overhead is really huge on platforms with a large number of CPUs.

Regards, Christian.

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-Sima

Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch