Message-ID: <CAGsJ_4xqDWu+AanD0RRMcAEtzje45p8WsaUtCtarO1nf4iECeQ@mail.gmail.com>
Date: Tue, 23 Dec 2025 10:12:44 +1300
From: Barry Song <21cnbao@...il.com>
To: Qinxin Xia <xiaqinxin@...wei.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 v5 2/3] dma-mapping: benchmark: add support for dma_map_sg

On Tue, Dec 23, 2025 at 4:33 AM Qinxin Xia <xiaqinxin@...wei.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.
>
> Reviewed-by: Barry Song <baohua@...nel.org>
> Signed-off-by: Qinxin Xia <xiaqinxin@...wei.com>
> ---
>  include/uapi/linux/map_benchmark.h |   1 +
>  kernel/dma/map_benchmark.c         | 117 ++++++++++++++++++++++++++++-
>  2 files changed, 117 insertions(+), 1 deletion(-)
>
> diff --git a/include/uapi/linux/map_benchmark.h b/include/uapi/linux/map_benchmark.h
> index e076748f2120..5fa3745e1651 100644
> --- a/include/uapi/linux/map_benchmark.h
> +++ b/include/uapi/linux/map_benchmark.h
> @@ -19,6 +19,7 @@
>
>  enum {
>         DMA_MAP_BENCH_SINGLE_MODE,
> +       DMA_MAP_BENCH_SG_MODE,
>         DMA_MAP_BENCH_MODE_MAX
>  };
>
> diff --git a/kernel/dma/map_benchmark.c b/kernel/dma/map_benchmark.c
> index a6345c10901c..76c0e1d5ff08 100644
> --- a/kernel/dma/map_benchmark.c
> +++ b/kernel/dma/map_benchmark.c
> @@ -16,6 +16,7 @@
>  #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>
>  #include <uapi/linux/map_benchmark.h>
> @@ -117,8 +118,121 @@ 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;
> +
> +       struct dma_sg_map_param *params = kzalloc(sizeof(*params), GFP_KERNEL);
> +
> +       if (!params)
> +               return NULL;
> +       /*
> +        * 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.
> +        */
> +       params->npages = map->bparam.granule;
> +       params->dma_dir = map->bparam.dma_dir;
> +       params->dev = map->dev;
> +       params->buf = kmalloc_array(params->npages, sizeof(*params->buf),
> +                                   GFP_KERNEL);
> +       if (!params->buf)
> +               goto out;
> +
> +       if (sg_alloc_table(&params->sgt, params->npages, GFP_KERNEL))
> +               goto free_buf;
> +
> +       for_each_sgtable_sg(&params->sgt, sg, i) {
> +               params->buf[i] = (void *)__get_free_page(GFP_KERNEL);
> +               if (!params->buf[i])
> +                       goto free_page;
> +
> +               sg_set_buf(sg, params->buf[i], PAGE_SIZE);
> +       }
> +
> +       return_ptr(params);
> +
> +free_page:
> +       while (i-- > 0)
> +               free_page((unsigned long)params->buf[i]);
> +
> +       sg_free_table(&params->sgt);
> +free_buf:
> +       kfree(params->buf);
> +out:
> +       return NULL;
> +}
> +
> +static void dma_sg_map_benchmark_unprepare(void *mparam)
> +{
> +       struct dma_sg_map_param *params = mparam;
> +       int i;
> +
> +       for (i = 0; i < params->npages; i++)
> +               free_page((unsigned long)params->buf[i]);
> +
> +       sg_free_table(&params->sgt);
> +
> +       kfree(params->buf);
> +       kfree(params);
> +}
> +
> +static void dma_sg_map_benchmark_prepare_data(void *mparam)
> +{
> +       struct dma_sg_map_param *params = mparam;
> +       struct scatterlist *sg;
> +       int i = 0;
> +
> +       if (params->dma_dir == DMA_FROM_DEVICE)
> +               return;
> +
> +       for_each_sgtable_sg(&params->sgt, sg, i)
> +               memset(params->buf[i], 0x66, PAGE_SIZE);
> +}
> +
> +static int dma_sg_map_benchmark_do_map(void *mparam)
> +{
> +       struct dma_sg_map_param *params = mparam;
> +       int ret = 0;
> +
> +       int sg_mapped = dma_map_sg(params->dev, params->sgt.sgl,
> +                                  params->npages, params->dma_dir);
> +       if (!sg_mapped) {
> +               pr_err("dma_map_sg failed on %s\n", dev_name(params->dev));
> +               ret = -ENOMEM;
> +       }
> +
> +       return ret;
> +}
> +
> +static void dma_sg_map_benchmark_do_unmap(void *mparam)
> +{
> +       struct dma_sg_map_param *params = mparam;
> +
> +       dma_unmap_sg(params->dev, params->sgt.sgl, params->npages,
> +                    params->dma_dir);
> +}
> +
> +static struct map_benchmark_ops dma_sg_map_benchmark_ops = {
> +       .prepare = dma_sg_map_benchmark_prepare,
> +       .unprepare = dma_sg_map_benchmark_unprepare,
> +       .prepare_data = dma_sg_map_benchmark_prepare_data,

Instead of using both prepare and prepare_data, which are ambiguous,
it would be better to rename prepare_data to initialize_data.

Thanks
Barry

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