> -----Original Message----- > From: Christian König <christian.koe...@amd.com> > Sent: Thursday, May 15, 2025 10:26 PM > To: wangtao <tao.wang...@honor.com>; sumit.sem...@linaro.org; > benjamin.gaign...@collabora.com; brian.star...@arm.com; > jstu...@google.com; tjmerc...@google.com > Cc: linux-me...@vger.kernel.org; dri-devel@lists.freedesktop.org; linaro- > mm-...@lists.linaro.org; linux-ker...@vger.kernel.org; > wangbintian(BintianWang) <bintian.w...@honor.com>; yipengxiang > <yipengxi...@honor.com>; liulu 00013167 <liulu....@honor.com>; hanfeng > 00012985 <feng....@honor.com> > Subject: Re: [PATCH 2/2] dmabuf/heaps: implement > DMA_BUF_IOCTL_RW_FILE for system_heap > > On 5/15/25 16:03, wangtao wrote: > > [wangtao] My Test Configuration (CPU 1GHz, 5-test average): > > Allocation: 32x32MB buffer creation > > - dmabuf 53ms vs. udmabuf 694ms (10X slower) > > - Note: shmem shows excessive allocation time > > Yeah, that is something already noted by others as well. But that is > orthogonal. > > > > > Read 1024MB File: > > - dmabuf direct 326ms vs. udmabuf direct 461ms (40% slower) > > - Note: pin_user_pages_fast consumes majority CPU cycles > > > > Key function call timing: See details below. > > Those aren't valid, you are comparing different functionalities here. > > Please try using udmabuf with sendfile() as confirmed to be working by T.J. [wangtao] Using buffer IO with dmabuf file read/write requires one memory copy. Direct IO removes this copy to enable zero-copy. The sendfile system call reduces memory copies from two (read/write) to one. However, with udmabuf, sendfile still keeps at least one copy, failing zero-copy.
If udmabuf sendfile uses buffer IO (file page cache), read latency matches dmabuf buffer read, but allocation time is much longer. With Direct IO, the default 16-page pipe size makes it slower than buffer IO. Test data shows: udmabuf direct read is much faster than udmabuf sendfile. dmabuf direct read outperforms udmabuf direct read by a large margin. Issue: After udmabuf is mapped via map_dma_buf, apps using memfd or udmabuf for Direct IO might cause errors, but there are no safeguards to prevent this. Allocate 32x32MB buffer and read 1024 MB file Test: Metric | alloc (ms) | read (ms) | total (ms) -----------------------|------------|-----------|----------- udmabuf buffer read | 539 | 2017 | 2555 udmabuf direct read | 522 | 658 | 1179 udmabuf buffer sendfile| 505 | 1040 | 1546 udmabuf direct sendfile| 510 | 2269 | 2780 dmabuf buffer read | 51 | 1068 | 1118 dmabuf direct read | 52 | 297 | 349 udmabuf sendfile test steps: 1. Open data file(1024MB), get back_fd 2. Create memfd(32MB) # Loop steps 2-6 3. Allocate udmabuf with memfd 4. Call sendfile(memfd, back_fd) 5. Close memfd after sendfile 6. Close udmabuf 7. Close back_fd > > Regards, > Christian.
