On Tue, Apr 9, 2024 at 12:34 AM Rong Qianfeng <11065417@xxxxxxxx> 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/drivers/dma-buf/heaps/system_heap.c#377 > 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. > > >
