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

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Message-ID: <cb1f418d-5c3e-4368-b13c-792b07b49087@huawei.com>
Date: Tue, 3 Feb 2026 10:45:57 +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 2026/1/30 17:16:08, Barry Song <21cnbao@...il.com> wrote:
> On Fri, Jan 30, 2026 at 4:38 PM Qinxin Xia <xiaqinxin@...wei.com> wrote:
>>
>>
>>
>> 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.
> 
> 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
>>
OK, I will update the documentation in the next version.
Do you have any other suggestions for this series?
-- 
Thanks,
Qinxin