linux-kernel - Re: [RFC RESEND 16/16] nvme-pci: use blk_rq_dma

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Date: Mon, 6 May 2024 09:25:01 +0200
From: Zhu Yanjun <yanjun.zhu@...ux.dev>
To: Leon Romanovsky <leon@...nel.org>
Cc: Christoph Hellwig <hch@....de>, Robin Murphy <robin.murphy@....com>,
 Marek Szyprowski <m.szyprowski@...sung.com>, Joerg Roedel <joro@...tes.org>,
 Will Deacon <will@...nel.org>, Jason Gunthorpe <jgg@...pe.ca>,
 Chaitanya Kulkarni <chaitanyak@...dia.com>,
 Chaitanya Kulkarni <kch@...dia.com>, Jonathan Corbet <corbet@....net>,
 Jens Axboe <axboe@...nel.dk>, Keith Busch <kbusch@...nel.org>,
 Sagi Grimberg <sagi@...mberg.me>, Yishai Hadas <yishaih@...dia.com>,
 Shameer Kolothum <shameerali.kolothum.thodi@...wei.com>,
 Kevin Tian <kevin.tian@...el.com>,
 Alex Williamson <alex.williamson@...hat.com>,
 Jérôme Glisse <jglisse@...hat.com>,
 Andrew Morton <akpm@...ux-foundation.org>, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
 linux-rdma@...r.kernel.org, iommu@...ts.linux.dev,
 linux-nvme@...ts.infradead.org, kvm@...r.kernel.org, linux-mm@...ck.org,
 Bart Van Assche <bvanassche@....org>,
 Damien Le Moal <damien.lemoal@...nsource.wdc.com>,
 Amir Goldstein <amir73il@...il.com>,
 "josef@...icpanda.com" <josef@...icpanda.com>,
 "Martin K. Petersen" <martin.petersen@...cle.com>,
 "daniel@...earbox.net" <daniel@...earbox.net>,
 Dan Williams <dan.j.williams@...el.com>, "jack@...e.com" <jack@...e.com>
Subject: Re: [RFC RESEND 16/16] nvme-pci: use blk_rq_dma_map() for NVMe SGL

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@...dia.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