Re: [PATCH v6 3/3] tools/dma: Add dma_map_sg support
From: Qinxin Xia
Date: Mon Feb 02 2026 - 21:46:37 EST
On 2026/1/30 17:16:08, Barry Song <21cnbao@xxxxxxxxx> wrote:
On Fri, Jan 30, 2026 at 4:38 PM Qinxin Xia <xiaqinxin@xxxxxxxxxx> wrote:OK, I will update the documentation in the next version.
On 2026/1/26 10:51:11, Barry Song <21cnbao@xxxxxxxxx> wrote:
On Mon, Jan 12, 2026 at 5:34 PM Qinxin Xia <xiaqinxin@xxxxxxxxxx> wrote:
Support for dma_map_sg, add option '-m' to distinguish mode.
i) Users can set option '-m' to select mode:
DMA_MAP_BENCH_SINGLE_MODE=0, DMA_MAP_BENCH_SG_MODE:=1
(The mode is also show in the test result).
ii) Users can set option '-g' to set sg_nents
(total count of entries in scatterlist)
the maximum number is 1024. Each of sg buf size is PAGE_SIZE.
e.g
[root@localhost]# ./dma_map_benchmark -m 1 -g 8 -t 8 -s 30 -d 2
dma mapping mode: DMA_MAP_BENCH_SG_MODE
dma mapping benchmark: threads:8 seconds:30 node:-1
dir:FROM_DEVICE granule/sg_nents: 8
average map latency(us):1.4 standard deviation:0.3
average unmap latency(us):1.3 standard deviation:0.3
[root@localhost]# ./dma_map_benchmark -m 0 -g 8 -t 8 -s 30 -d 2
dma mapping mode: DMA_MAP_BENCH_SINGLE_MODE
dma mapping benchmark: threads:8 seconds:30 node:-1
dir:FROM_DEVICE granule/sg_nents: 8
average map latency(us):1.0 standard deviation:0.3
average unmap latency(us):1.3 standard deviation:0.5
What happens if m is set to 0 while g is set to 8?
Thanks
Barry
Hi Barry!
m set '0' and g set '8', This means that 8 page_sizes are mapped at a
time in single mode.
As the comment for the struct map_benchmark definition says:
__u32 granule; /* how many PAGE_SIZE will do map/unmap once a time */
[root@localhost xqx]# ./dma_map_benchmark -m 0 -g 8 -t 8 -s 30 -d 2
dma mapping benchmark(SINGLE_MODE): threads:8 seconds:30 node:-1
dir:FROM_DEVICE granule:8
average map latency(us):0.2 standard deviation:0.1
average unmap latency(us):4.3 standard deviation:1.4
======================================================
The newly added sg mode reuses the -g option as sgnents and is described
in the comments:
/*
* Set the number of scatterlist entries based on the granule.
* In SG mode, 'granule' represents the number of scatterlist
entries.
* Each scatterlist entry corresponds to a single page.
*/
By the way, I've considered testing sgnents of different sizes, but it's
not very easy to set for user parameters, so I set it with each
scatterlist entry corresponds to a single page.
This is a bit odd. Ideally, we shouldn’t have a mixed definition
for a single variant, but since this is just a tool, it may be
acceptable.
That said, the documentation should at least be updated in
patches 2/3 and 3/3. As it stands, it still says:
__u32 granule; /* how many PAGE_SIZE are mapped or unmapped
at a time */
Thanks,
Qinxin
Do you have any other suggestions for this series?
--
Thanks,
Qinxin