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

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Message-ID: <Zqiqv7fomIp1IPS_@phenom.ffwll.local>
Date: Tue, 30 Jul 2024 10:56:31 +0200
From: Daniel Vetter <daniel.vetter@...ll.ch>
To: Huan Yang <link@...o.com>
Cc: 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

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
needlessly serialization operations.

The other issue is that the mmap has some overhead, but might not be too
bad.
-Sima
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch