Re: [RFC PATCH for-next 3/3] libhns: Add support for SVE Direct WQE function

["xuhaoyue (A)" <xuhaoyue1@hisilicon.com>]

On 2023/3/30 21:01:20, Jason Gunthorpe wrote:
> On Thu, Mar 30, 2023 at 08:57:41PM +0800, xuhaoyue (A) wrote:
>>
>>
>> On 2023/3/27 20:55:59, Jason Gunthorpe wrote:
>>> On Mon, Mar 27, 2023 at 08:53:35PM +0800, xuhaoyue (A) wrote:
>>>
>>>>>>  static void hns_roce_write512(uint64_t *dest, uint64_t *val)
>>>>>>  {
>>>>>>  	mmio_memcpy_x64(dest, val, sizeof(struct hns_roce_rc_sq_wqe));
>>>>>> @@ -314,7 +319,10 @@ static void hns_roce_write_dwqe(struct hns_roce_qp *qp, void *wqe)
>>>>>>  	hr_reg_write(rc_sq_wqe, RCWQE_DB_SL_H, qp->sl >> HNS_ROCE_SL_SHIFT);
>>>>>>  	hr_reg_write(rc_sq_wqe, RCWQE_WQE_IDX, qp->sq.head);
>>>>>>  
>>>>>> -	hns_roce_write512(qp->sq.db_reg, wqe);
>>>>>> +	if (qp->flags & HNS_ROCE_QP_CAP_SVE_DIRECT_WQE)
>>>>>
>>>>> Why do you need a device flag here?
>>>>
>>>> Our CPU die can support NEON instructions and SVE instructions,
>>>> but some CPU dies only have SVE instructions that can accelerate our direct WQE performance.
>>>> Therefore, we need to add such a flag bit to distinguish.
>>>
>>> NEON vs SVE is available to userspace already, it shouldn't come
>>> throuhg a driver flag. You need another reason to add this flag
>>>
>>> The userspace should detect the right instruction to use based on the
>>> cpu flags using the attribute stuff I pointed you at
>>>
>>> Jason
>>> .
>>>
>>
>> We optimized direct wqe based on different instructions for
>> different CPUs, but the architecture of the CPUs is the same and
>> supports both SVE and NEON instructions.  We plan to use cpuid to
>> distinguish between them. Is this more reasonable?
> 
> Uhh, do you mean certain CPUs won't work with SVE and others won't
> work with NEON?
> 
> That is quite horrible
> 
> Jason
> .
> 

No, acctually for general scenarios, our CPU supports two types of instructions, SVE and NEON.
However, for the CPU that requires high fp64 floating-point computing power, the SVE instruction is enhanced and the NEON instruction is weakened.

Sincerely,
Haoyue