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

Daniel Vetter
2024-07-31T20:46:26Z

On Tue, Jul 30, 2024 at 08:04:04PM +0800, Huan Yang wrote:
>
> 在 2024/7/30 17:05, Huan Yang 写道:
> >
> > 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
>
> 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.

Ok that's almost the throughput of your patch set, which I think is close
enough. The remaining difference is probably just the mmap overhead, not
sure whether/how we can do direct i/o to an fd directly ... in principle
it's possible for any file that uses the standard pagecache.
-Sima
--
Daniel Vetter
Software Engineer, Intel Corporation