On 5/16/25 09:40, wangtao wrote:
-----Original Message----- From: Christian König christian.koenig@amd.com Sent: Thursday, May 15, 2025 10:26 PM To: wangtao tao.wangtao@honor.com; sumit.semwal@linaro.org; benjamin.gaignard@collabora.com; Brian.Starkey@arm.com; jstultz@google.com; tjmercier@google.com Cc: linux-media@vger.kernel.org; dri-devel@lists.freedesktop.org; linaro- mm-sig@lists.linaro.org; linux-kernel@vger.kernel.org; wangbintian(BintianWang) bintian.wang@honor.com; yipengxiang yipengxiang@honor.com; liulu 00013167 liulu.liu@honor.com; hanfeng 00012985 feng.han@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 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:
- Open data file(1024MB), get back_fd
- Create memfd(32MB) # Loop steps 2-6
- Allocate udmabuf with memfd
- Call sendfile(memfd, back_fd)
- Close memfd after sendfile
- Close udmabuf
- Close back_fd
Regards, Christian.
On Fri, May 16, 2025 at 1:36 AM Christian König christian.koenig@amd.com wrote:
On 5/16/25 09:40, wangtao wrote:
-----Original Message----- From: Christian König christian.koenig@amd.com Sent: Thursday, May 15, 2025 10:26 PM To: wangtao tao.wangtao@honor.com; sumit.semwal@linaro.org; benjamin.gaignard@collabora.com; Brian.Starkey@arm.com; jstultz@google.com; tjmercier@google.com Cc: linux-media@vger.kernel.org; dri-devel@lists.freedesktop.org; linaro- mm-sig@lists.linaro.org; linux-kernel@vger.kernel.org; wangbintian(BintianWang) bintian.wang@honor.com; yipengxiang yipengxiang@honor.com; liulu 00013167 liulu.liu@honor.com; hanfeng 00012985 feng.han@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:
- Open data file(1024MB), get back_fd
- Create memfd(32MB) # Loop steps 2-6
- Allocate udmabuf with memfd
- Call sendfile(memfd, back_fd)
- Close memfd after sendfile
- Close udmabuf
- Close back_fd
Regards, Christian.
linaro-mm-sig@lists.linaro.org
-
Christian König -
T.J. Mercier