Re: [PATCH for-next 1/2] RDMA/hns: Add the workqueue framework for flush cqe handler

["Liuyixian (Eason)" <liuyixian@huawei.com>]

On 2019/11/8 2:28, Jason Gunthorpe wrote:
> On Thu, Nov 07, 2019 at 08:48:25PM +0800, Liuyixian (Eason) wrote:
>>
>>
>> On 2019/11/7 4:40, Jason Gunthorpe wrote:
>>> On Mon, Oct 28, 2019 at 05:45:44PM +0800, Yixian Liu wrote:
>>>> @@ -1998,6 +2000,17 @@ static int hns_roce_v2_init(struct hns_roce_dev *hr_dev)
>>>>  		}
>>>>  	}
>>>>  
>>>> +	snprintf(workq_name, HNS_ROCE_WORKQ_NAME_LEN - 1,
>>>> +		 "hns_roce_%d_flush_wq", device_id);
>>>> +	device_id++;
>>>> +
>>>> +	hr_dev->flush_workq = alloc_workqueue(workq_name, WQ_HIGHPRI, 0);
>>>> +	if (!hr_dev->flush_workq) {
>>>
>>> Why is this so time critical?
>>
>> Hi Jason,
>>
>> I am not quite sure whether you concerned with the flag "WQ_HIGHPRI" or
>> why WQ is created in hns_roce_v2_init.
> 
> Yes, why do you need a dedicated HIGHPRI work queue.

As hip08 hardware needs driver to help to do flush operation, I am not
sure the application can perceive that qp state is error without receiving
flush cqe if work in WQ is not scheduled in time.

> 
>> If it is WQ_HIGHPRI, yes, it is much better to implement flush operation
>> ASAP to help generating flushed cqe as ULP may poll cqe urgently. If you
>> concerned allocation stage, as flush operation is support for hip08 only,
>> there is no other place proper than here I think.
> 
> Why? This is only something that happens in error cases.

Yes, maybe we can move out WQ_HIGHPRI flag safely, will fix it in v2.

> 
>>> Why don't you do this from hns_roce_irq_work_handle() ?
>>
>> As described in the cover letter, here we used CMWQ (concurrency management workqueue)
>> to make sure that flush operation can be implemented ASAP. Current irq workqueue is
>> a singlethread workqueue, which may delay the flush too long when the system is heavy.
>>
>> Do you mean we can change irq workqueue to CMWQ to put flush work into it?
> 
> As far as I could tell the only thing the triggered the work to run
> was some variable which was only set in another work queue 'hns_roce_irq_work_handle()'

OK, thanks. I will consider you suggestion and reuse the irq workqueue.

>  
>>>> +}
>>>> +
>>>> +void init_flush_work(struct hns_roce_dev *hr_dev, struct hns_roce_qp *hr_qp)
>>>> +{
>>>> +	struct hns_roce_flush_work *flush_work;
>>>> +
>>>> +	flush_work = kzalloc(sizeof(struct hns_roce_flush_work), GFP_ATOMIC);
>>>> +	if (!flush_work)
>>>> +		return;
>>>
>>> Don't do things that can fail here
>>
>> Do you mean that as "GFP_ATOMIC" is used, the if branch can be deleted?
> 
> No, don't do allocations at all if you can't allow them to fail.

OK, thanks! I will initialize this structure at compile time.

> 
> Jason
> 
> .
>