On Tue, Apr 9, 2024 at 12:34 AM Rong Qianfeng 11065417@vivo.com wrote:
在 2024/4/8 15:58, Christian König 写道:
Am 07.04.24 um 09:50 schrieb Rong Qianfeng:
[SNIP]
Am 13.11.21 um 07:22 schrieb Jianqun Xu:
Add DMA_BUF_IOCTL_SYNC_PARTIAL support for user to sync dma-buf with offset and len.
You have not given an use case for this so it is a bit hard to review. And from the existing use cases I don't see why this should be necessary.
Even worse from the existing backend implementation I don't even see how drivers should be able to fulfill this semantics.
Please explain further, Christian.
Here is a practical case: The user space can allocate a large chunk of dma-buf for self-management, used as a shared memory pool. Small dma-buf can be allocated from this shared memory pool and released back to it after use, thus improving the speed of dma-buf allocation and release. Additionally, custom functionalities such as memory statistics and boundary checking can be implemented in the user space. Of course, the above-mentioned functionalities require the implementation of a partial cache sync interface.
Well that is obvious, but where is the code doing that?
You can't send out code without an actual user of it. That will obviously be rejected.
Regards, Christian.
In fact, we have already used the user-level dma-buf memory pool in the camera shooting scenario on the phone.
From the test results, The execution time of the photo shooting algorithm has been reduced from 3.8s to 3s.
For phones, the (out of tree) Android version of the system heap has a page pool connected to a shrinker. That allows you to skip page allocation without fully pinning the memory like you get when allocating a dma-buf that's way larger than necessary. If it's for a camera maybe you need physically contiguous memory, but it's also possible to set that up.
https://android.googlesource.com/kernel/common/+/refs/heads/android14-6.1/dr...
To be honest, I didn't understand your concern "...how drivers should be able to fulfill this semantics." Can you please help explain it in more detail?
Thanks,
Rong Qianfeng.
Thanks Rong Qianfeng.