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

[Christian König]

Am 30.07.24 um 11:05 schrieb Huan Yang:
> 在 2024/7/30 16:56, Daniel Vetter 写道:
> > [????????? daniel.vetter@xxxxxxxx ????????? 
> > 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.

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.

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