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Date:   Mon, 22 Nov 2021 13:10:05 +0200
From:   Leon Romanovsky <leon@kernel.org>
To:     Wenpeng Liang <liangwenpeng@huawei.com>
Cc:     jgg@nvidia.com, linux-rdma@vger.kernel.org, linuxarm@huawei.com
Subject: Re: [PATCH v4 for-next 1/1] RDMA/hns: Support direct wqe of userspace
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References: <20211122033801.30807-1-liangwenpeng@huawei.com>
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On Mon, Nov 22, 2021 at 05:28:31PM +0800, Wenpeng Liang wrote:
> 
> 
> On 2021/11/22 16:58, Leon Romanovsky wrote:
> >>  	entry = to_hns_mmap(rdma_entry);
> >>  	pfn = entry->address >> PAGE_SHIFT;
> >> -	prot = vma->vm_page_prot;
> >>  
> >> -	if (entry->mmap_type != HNS_ROCE_MMAP_TYPE_TPTR)
> >> -		prot = pgprot_noncached(prot);
> >> +	switch (entry->mmap_type) {
> >> +	case HNS_ROCE_MMAP_TYPE_DB:
> >> +		prot = pgprot_noncached(vma->vm_page_prot);
> >> +		break;
> >> +	case HNS_ROCE_MMAP_TYPE_TPTR:
> >> +		prot = vma->vm_page_prot;
> >> +		break;
> >> +	case HNS_ROCE_MMAP_TYPE_DWQE:
> >> +		prot = pgprot_device(vma->vm_page_prot);
> > Everything fine, except this pgprot_device(). You probably need to check
> > WC internally in your driver and use or pgprot_writecombine() or
> > pgprot_noncached() explicitly.
> > 
> > Thanks
> > .
> > 
> 
> This issue is also discussed in the v2 version, direct wqe uses
> this prot on HIP09 can achieve better performance than NC.
> 
> v2 link: https://patchwork.kernel.org/project/linux-rdma/patch/1622705834-19353-3-git-send-email-liweihang@huawei.com/

But isn't it specific to ARM model that behaves such? Will it be the case
when you move to upgrade your ARM core?

Thanks

> 
> Thanks
> Wenpeng