linux-kernel - Re: [PATCH v2 for-next 2/2] RDMA/hns: Support userspace configuring congestion control algorithm with QP granularity

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Date: Mon, 26 Feb 2024 10:06:47 -0400
From: Jason Gunthorpe <jgg@...pe.ca>
To: Junxian Huang <huangjunxian6@...ilicon.com>
Cc: leon@...nel.org, linux-rdma@...r.kernel.org, linuxarm@...wei.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 for-next 2/2] RDMA/hns: Support userspace configuring
 congestion control algorithm with QP granularity

On Thu, Feb 22, 2024 at 03:06:20PM +0800, Junxian Huang wrote:
> >> +enum hns_roce_congest_type_flags {
> >> +	HNS_ROCE_CREATE_QP_FLAGS_DCQCN = 1 << 0,
> >> +	HNS_ROCE_CREATE_QP_FLAGS_LDCP = 1 << 1,
> >> +	HNS_ROCE_CREATE_QP_FLAGS_HC3 = 1 << 2,
> >> +	HNS_ROCE_CREATE_QP_FLAGS_DIP = 1 << 3,
> >> +};
> > 
> > Why are these bit flags if they are exclusive?
> > 
> 
> Our FW uses bit flags. Although there is no direct relationship between
> FW and ABI, but from the perspective of readability, bit flags are also
> used consistently here in ABI.

Don't do that in uapi.

> >> +enum hns_roce_create_qp_comp_mask {
> >> +	HNS_ROCE_CREATE_QP_MASK_CONGEST_TYPE = 1 << 1,
> > 
> > Why 1<<1 not 1<<0?
> 
> This is to keep consistent with our internal ABI, there are some
> features not upstream yet.

Nope, pack them tightly. Don't keep an "internal ABI"

> >> @@ -114,6 +128,9 @@ struct hns_roce_ib_alloc_ucontext_resp {
> >>  	__u32	reserved;
> >>  	__u32	config;
> >>  	__u32	max_inline_data;
> >> +	__u8	reserved0;
> >> +	__u8	congest_type;
> > 
> > Why this layout?
> 
> Same as the 1<<1 issue, to keep consistent with our internal ABI.

Same answer

Jason