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Date: Mon, 6 May 2024 09:25:01 +0200
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Subject: Re: [RFC RESEND 16/16] nvme-pci: use blk_rq_dma_map() for NVMe SGL
To: Leon Romanovsky <leon@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>, Robin Murphy <robin.murphy@arm.com>,
 Marek Szyprowski <m.szyprowski@samsung.com>, Joerg Roedel <joro@8bytes.org>,
 Will Deacon <will@kernel.org>, Jason Gunthorpe <jgg@ziepe.ca>,
 Chaitanya Kulkarni <chaitanyak@nvidia.com>,
 Chaitanya Kulkarni <kch@nvidia.com>, Jonathan Corbet <corbet@lwn.net>,
 Jens Axboe <axboe@kernel.dk>, Keith Busch <kbusch@kernel.org>,
 Sagi Grimberg <sagi@grimberg.me>, Yishai Hadas <yishaih@nvidia.com>,
 Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>,
 Kevin Tian <kevin.tian@intel.com>,
 Alex Williamson <alex.williamson@redhat.com>,
 =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= <jglisse@redhat.com>,
 Andrew Morton <akpm@linux-foundation.org>, linux-doc@vger.kernel.org,
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 linux-rdma@vger.kernel.org, iommu@lists.linux.dev,
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 Bart Van Assche <bvanassche@acm.org>,
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 Amir Goldstein <amir73il@gmail.com>,
 "josef@toxicpanda.com" <josef@toxicpanda.com>,
 "Martin K. Petersen" <martin.petersen@oracle.com>,
 "daniel@iogearbox.net" <daniel@iogearbox.net>,
 Dan Williams <dan.j.williams@intel.com>, "jack@suse.com" <jack@suse.com>
References: <cover.1709635535.git.leon@kernel.org>
 <016fc02cbfa9be3c156a6f74df38def1e09c08f1.1709635535.git.leon@kernel.org>
 <c9f9e29e-c2e1-4f99-b359-db0babd41dec@linux.dev>
 <20240505132314.GC68202@unreal>
Content-Language: en-US
From: Zhu Yanjun <yanjun.zhu@linux.dev>
In-Reply-To: <20240505132314.GC68202@unreal>
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On 05.05.24 15:23, Leon Romanovsky wrote:
> On Fri, May 03, 2024 at 04:41:21PM +0200, Zhu Yanjun wrote:
>> On 05.03.24 12:18, Leon Romanovsky wrote:
>>> From: Chaitanya Kulkarni <kch@nvidia.com>
> <...>
>
>>> This is an RFC to demonstrate the newly added DMA APIs can be used to
>>> map/unmap bvecs without the use of sg list, hence I've modified the pci
>>> code to only handle SGLs for now. Once we have some agreement on the
>>> structure of new DMA API I'll add support for PRPs along with all the
>>> optimization that I've removed from the code for this RFC for NVMe SGLs
>>> and PRPs.
>>>
> <...>
>
>>> diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
>>> index e6267a6aa380..140939228409 100644
>>> --- a/drivers/nvme/host/pci.c
>>> +++ b/drivers/nvme/host/pci.c
>>> @@ -236,7 +236,9 @@ struct nvme_iod {
>>>    	unsigned int dma_len;	/* length of single DMA segment mapping */
>>>    	dma_addr_t first_dma;
>>>    	dma_addr_t meta_dma;
>>> -	struct sg_table sgt;
>>> +	struct dma_iova_attrs iova;
>>> +	dma_addr_t dma_link_address[128];
>> Why the length of this array is 128? Can we increase this length of the
>> array?
> It is combination of two things:
>   * Good enough value for this nvme RFC to pass simple test, which Chaitanya did.
>   * Output of various NVME_CTRL_* defines

Thanks a lot. I enlarged this number to 512. It seems that it can work. 
Hope this will increase the performance.

Best Regards,

Zhu Yanjun

>
> Thanks

-- 
Best Regards,
Yanjun.Zhu