Re: [PATCH 2/3] dma-mapping: benchmark: add support for dma_map_sg

[Qinxin Xia <xiaqinxin@huawei.com>]

在 2025/4/7 13:50, Barry Song 写道:
> On Wed, Feb 12, 2025 at 3:27 PM Qinxin Xia <xiaqinxin@huawei.com> wrote:
>> Support for dma scatter-gather mapping and is intended for testing
>> mapping performance. It achieves by introducing the dma_sg_map_param
>> structure and related functions, which enable the implementation of
>> scatter-gather mapping preparation, mapping, and unmapping operations.
>> Additionally, the dma_map_benchmark_ops array is updated to include
>> operations for scatter-gather mapping. This commit aims to provide
>> a wider range of mapping performance test  to cater to different scenarios.
>>
>> Signed-off-by: Qinxin Xia <xiaqinxin@huawei.com>
>> ---
>>   include/linux/map_benchmark.h |   1 +
>>   kernel/dma/map_benchmark.c    | 102 ++++++++++++++++++++++++++++++++++
>>   2 files changed, 103 insertions(+)
>>
>> diff --git a/include/linux/map_benchmark.h b/include/linux/map_benchmark.h
>> index 054db02a03a7..a9c1a104ba4f 100644
>> --- a/include/linux/map_benchmark.h
>> +++ b/include/linux/map_benchmark.h
>> @@ -17,6 +17,7 @@
>>
>>   enum {
>>          DMA_MAP_SINGLE_MODE,
>> +       DMA_MAP_SG_MODE,
>>          DMA_MAP_MODE_MAX
>>   };
>>
>> diff --git a/kernel/dma/map_benchmark.c b/kernel/dma/map_benchmark.c
>> index d8ec0ce058d8..b5828eeb3db7 100644
>> --- a/kernel/dma/map_benchmark.c
>> +++ b/kernel/dma/map_benchmark.c
>> @@ -17,6 +17,7 @@
>>   #include <linux/module.h>
>>   #include <linux/pci.h>
>>   #include <linux/platform_device.h>
>> +#include <linux/scatterlist.h>
>>   #include <linux/slab.h>
>>   #include <linux/timekeeping.h>
>>
>> @@ -111,8 +112,109 @@ static struct map_benchmark_ops dma_single_map_benchmark_ops = {
>>          .do_unmap = dma_single_map_benchmark_do_unmap,
>>   };
>>
>> +struct dma_sg_map_param {
>> +       struct sg_table sgt;
>> +       struct device *dev;
>> +       void **buf;
>> +       u32 npages;
>> +       u32 dma_dir;
>> +};
>> +
>> +static void *dma_sg_map_benchmark_prepare(struct map_benchmark_data *map)
>> +{
>> +       struct scatterlist *sg;
>> +       int i = 0;
>> +
>> +       struct dma_sg_map_param *mparam __free(kfree) = kzalloc(sizeof(*mparam), GFP_KERNEL);
>> +       if (!mparam)
>> +               return NULL;
>> +
>> +       mparam->npages = map->bparam.granule;
> Please add comments explaining that "granule" serves as  nents in SG
> mode, and that each SG entry corresponds to a single page.
> Otherwise, in single mode, the granule represents what we map and
> unmap as a whole in a single operation.
> I mean, make the code below clearly express what you are doing:
>
> __u32 granule;  /* how many PAGE_SIZE will do map/unmap once a time */
>
Okay, I'll add comments here in next version, thank you for your advice!
>> +       mparam->dma_dir = map->bparam.dma_dir;
>> +       mparam->dev = map->dev;
>> +       mparam->buf = kmalloc_array(mparam->npages, sizeof(*mparam->buf),
>> +                                   GFP_KERNEL);
>> +       if (!mparam->buf)
>> +               goto err1;
>> +
>> +       if (sg_alloc_table(&mparam->sgt, mparam->npages, GFP_KERNEL))
>> +               goto err2;
>> +
>> +       for_each_sgtable_sg(&mparam->sgt, sg, i) {
>> +               mparam->buf[i] = (void *)__get_free_page(GFP_KERNEL);
>> +               if (!mparam->buf[i])
>> +                       goto err3;
>> +
>> +               if (mparam->dma_dir != DMA_FROM_DEVICE)
>> +                       memset(mparam->buf[i], 0x66, PAGE_SIZE);
>> +
>> +               sg_set_buf(sg, mparam->buf[i], PAGE_SIZE);
>> +       }
>> +
>> +       return_ptr(mparam);
>> +
>> +err3:
>> +       while (i-- > 0)
>> +               free_page((unsigned long)mparam->buf[i]);
>> +
>> +       pr_err("dma_map_sg failed get free page on %s\n", dev_name(mparam->dev));
>> +       sg_free_table(&mparam->sgt);
>> +err2:
>> +       pr_err("dma_map_sg failed alloc sg table on %s\n", dev_name(mparam->dev));
>> +       kfree(mparam->buf);
>> +err1:
>> +       pr_err("dma_map_sg failed alloc mparam buf on %s\n", dev_name(mparam->dev));
>> +       return NULL;
> I assume allocation failures will already trigger their own warnings, so your
> pr_err isn't necessary. BTW, please replace err1, err2, err3 with something
> meaningful.
Okay, I'll delete these unnecessary prints and make the label changes 
more meaningful in the next version.
>> +}
>> +
>> +static void dma_sg_map_benchmark_unprepare(void *arg)
>> +{
>> +       struct dma_sg_map_param *mparam = arg;
>> +       int i;
>> +
>> +       for (i = 0; i < mparam->npages; i++)
>> +               free_page((unsigned long)mparam->buf[i]);
>> +
>> +       sg_free_table(&mparam->sgt);
>> +
>> +       kfree(mparam->buf);
>> +       kfree(mparam);
>> +}
>> +
>> +static int dma_sg_map_benchmark_do_map(void *arg)
>> +{
>> +       struct dma_sg_map_param *mparam = arg;
>> +
>> +       int sg_mapped = dma_map_sg(mparam->dev, mparam->sgt.sgl,
>> +                                  mparam->npages, mparam->dma_dir);
>> +       if (!sg_mapped) {
>> +               pr_err("dma_map_sg failed on %s\n", dev_name(mparam->dev));
>> +               return -ENOMEM;
>> +       }
>> +
>> +       return 0;
>> +}
>> +
>> +static int dma_sg_map_benchmark_do_unmap(void *arg)
> void
Initially for future expansion considerations, but I think, as you 
suggested, we could make it 'void' first.
>> +{
>> +       struct dma_sg_map_param *mparam = arg;
>> +
>> +       dma_unmap_sg(mparam->dev, mparam->sgt.sgl, mparam->npages,
>> +                    mparam->dma_dir);
>> +
>> +       return 0;
> drop it.
Okay, I'll fix it in the next version.
>> +}
>> +
>> +static struct map_benchmark_ops dma_sg_map_benchmark_ops = {
>> +       .prepare = dma_sg_map_benchmark_prepare,
>> +       .unprepare = dma_sg_map_benchmark_unprepare,
>> +       .do_map = dma_sg_map_benchmark_do_map,
>> +       .do_unmap = dma_sg_map_benchmark_do_unmap,
>> +};
>> +
>>   static struct map_benchmark_ops *dma_map_benchmark_ops[DMA_MAP_MODE_MAX] = {
>>          [DMA_MAP_SINGLE_MODE] = &dma_single_map_benchmark_ops,
>> +       [DMA_MAP_SG_MODE] = &dma_sg_map_benchmark_ops,
>>   };
>>
>>   static int map_benchmark_thread(void *data)
>> --
>> 2.33.0
>>
> Thanks
> Barry