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Message-ID: <8ce18336-0bd8-4c6f-8c34-4496c76351ac@huawei.com>
Date: Tue, 1 Apr 2025 20:46:53 +0800
From: Qinxin Xia <xiaqinxin@...wei.com>
To: Barry Song <21cnbao@...il.com>
CC: yangyicong <yangyicong@...wei.com>, "hch@....de" <hch@....de>,
"iommu@...ts.linux.dev" <iommu@...ts.linux.dev>, Jonathan Cameron
<jonathan.cameron@...wei.com>, "Zengtao (B)" <prime.zeng@...ilicon.com>,
"fanghao (A)" <fanghao11@...wei.com>, "linux-kernel@...r.kernel.org"
<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] dma-mapping: benchmark: add support for dma_map_sg
在 2025/3/6 17:28, Barry Song 写道:
> On Wed, Mar 5, 2025 at 2:49 AM Qinxin Xia <xiaqinxin@...wei.com> wrote:
>>
>> 在 2025/2/22 14:36, Barry Song 写道:
>>> On Fri, Feb 21, 2025 at 4:16 PM xiaqinxin <xiaqinxin@...wei.com> wrote:
>>>>
>>>> -----邮件原件-----
>>>> 发件人: Barry Song <21cnbao@...il.com>
>>>> 发送时间: 2025年2月18日 4:59
>>>> 收件人: xiaqinxin <xiaqinxin@...wei.com>
>>>> 抄送: chenxiang66@...ilicon.com; yangyicong <yangyicong@...wei.com>; hch@....de; iommu@...ts.linux.dev; Jonathan Cameron <jonathan.cameron@...wei.com>; Zengtao (B) <prime.zeng@...ilicon.com>; fanghao (A) <fanghao11@...wei.com>; linux-kernel@...r.kernel.org
>>>> 主题: Re: [PATCH 2/3] dma-mapping: benchmark: add support for dma_map_sg
>>>>
>>>> On Wed, Feb 12, 2025 at 3:27 PM 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.
>>>> This benchmark is mainly designed to debug contention issues, such as IOMMU TLB flushes or IOMMU driver bottlenecks. I don't fully understand how SG or single will impact the evaluation of the IOMMU driver, making it unclear if the added complexity is justified.
>>>>
>>>> Can you add some explanation on why single mode is not sufficient for profiling and improving IOMMU drivers?
>>>>
>>>> Hello Barry ! 😊
>>>> Currently, the HiSilicon accelerator service uses the dma_map_sg interface. We want to evaluate the performance of the entire DMA map process. (including not only the iommu, but also the map framework). In addition, for scatterlist, __iommu_map is executed for each nent. This increases the complexity and time overhead of mapping. The effect of this fragmentation is not obvious in dma_map_single, which only handles a single contiguous block of memory.
>>>>
>>> Thanks!
>>> Please update your editor to ensure it doesn't respond with such long sentences
>>> without line breaks in the future :-)
>> Hello Barry !
>>
>> Thank you for your advice, I will I'll pay attention. Leon
>>
>>> Can you provide concrete examples or data showing how the newly added mode
>>> improves profiling of the entire DMA map process? For instance, what limitations
>>> exist without this mode? What performance issues cannot be identified without
>>> it?
>> You can see this patch
>> :https://lore.kernel.org/all/cover.1738765879.git.leonro@nvidia.com/
>>
>> Leon provides new interface for scatterlist scenarios to improve
>> performance and gives some
>>
>> application instance in rdma and vfio. Users can use dma_map_sg
>> benchmark to measure
>>
>> the performance improvement of the optimized interface compared with the
>> previous one.
> I’m not quite sure how this patchset helps compare the new interfaces—
> dma_iova_try_alloc(), dma_iova_link(), dma_iova_destroy()—with
> dma_map_sg(), dma_unmap_sg(), etc. Does this mean you also plan
> to include these new interfaces in the benchmark?
>
> However, I agree that this patchset could be useful for evaluating cases
> where we are optimizing dma_map_sg itself for A/B side testing. Do we
> have such a case?
Hello Barry !
I'm sorry, I haven't responded for so long, something urgent took up my
time,
and we've had some discussion about the requirement scenario.
CCA precision computing calls dma_map_sg and reuses the swiotlb process.
Our team and HUAWEI CLOUD are trying to optimize this process, such as
this patch:
https://lwn.net/ml/linux-kernel/cover.1690871004.git.petr.tesarik.ext@huawei.com/,
dma_map_sg benchmark provides a test method to evaluate performance results.
Thank you !
>> Thanks!
>>
>>>>> Signed-off-by: Qinxin Xia <xiaqinxin@...wei.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;
>>>>> + 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;
>>>>> +}
>>>>> +
>>>>> +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) {
>>>>> + struct dma_sg_map_param *mparam = arg;
>>>>> +
>>>>> + dma_unmap_sg(mparam->dev, mparam->sgt.sgl, mparam->npages,
>>>>> + mparam->dma_dir);
>>>>> +
>>>>> + return 0;
>>>>> +}
>>>>> +
>>>>> +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
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