On Fri, May 16, 2025 at 1:36 AM Christian König <christian.koe...@amd.com> wrote: > > On 5/16/25 09:40, wangtao wrote: > > > > > >> -----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. > > > Then please work on fixing this. > > Regards, > Christian. > > > > > > 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
I can't reproduce the part where udmabuf direct reads are faster than buffered reads. That's the opposite of what I'd expect. Something seems wrong with those buffered reads. > > udmabuf buffer sendfile| 505 | 1040 | 1546 > > udmabuf direct sendfile| 510 | 2269 | 2780 I can reproduce the 3.5x slower udambuf direct sendfile compared to udmabuf direct read. It's a pretty disappointing result, so it seems like something could be improved there. 1G from ext4 on 6.12.17 | read/sendfile (ms) ------------------------|------------------- udmabuf buffer read | 351 udmabuf direct read | 540 udmabuf buffer sendfile | 255 udmabuf direct sendfile | 1990 > > 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. > > >
