linux-kernel - Re: [PATCH v6 3/3] tools/dma: Add dma_map

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Message-ID: <4794d927-6de4-4283-b3ee-ee5030941a72@huawei.com>
Date: Fri, 30 Jan 2026 16:38:15 +0800
From: Qinxin Xia <xiaqinxin@...wei.com>
To: Barry Song <21cnbao@...il.com>
CC: <jonathan.cameron@...wei.com>, <wangzhou1@...ilicon.com>,
	<iommu@...ts.linux.dev>, <prime.zeng@...wei.com>, <fanghao11@...wei.com>,
	<linux-kernel@...r.kernel.org>, <linuxarm@...wei.com>
Subject: Re: [PATCH v6 3/3] tools/dma: Add dma_map_sg support



On 2026/1/26 10:51:11, Barry Song <21cnbao@...il.com> wrote:
> On Mon, Jan 12, 2026 at 5:34 PM Qinxin Xia <xiaqinxin@...wei.com> 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@...alhost]# ./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@...alhost]# ./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@...alhost 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.

Thanks,
Qinxin