linux-kernel - Re: [RFC PATCH rdma-next 08/10] RDMA/rxe: Implement flush execution in responder side

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Date:   Tue, 11 Jan 2022 05:34:36 +0000
From:   "lizhijian@...itsu.com" <lizhijian@...itsu.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
CC:     "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "zyjzyj2000@...il.com" <zyjzyj2000@...il.com>,
        "aharonl@...dia.com" <aharonl@...dia.com>,
        "leon@...nel.org" <leon@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "mbloch@...dia.com" <mbloch@...dia.com>,
        "liangwenpeng@...wei.com" <liangwenpeng@...wei.com>,
        "yangx.jy@...itsu.com" <yangx.jy@...itsu.com>,
        "rpearsonhpe@...il.com" <rpearsonhpe@...il.com>,
        "y-goto@...itsu.com" <y-goto@...itsu.com>
Subject: Re: [RFC PATCH rdma-next 08/10] RDMA/rxe: Implement flush execution
 in responder side



On 10/01/2022 22:34, Jason Gunthorpe wrote:
> On Mon, Jan 10, 2022 at 05:45:47AM +0000, lizhijian@...itsu.com wrote:
>> Hi Jason
>>
>>
>> On 07/01/2022 01:33, Jason Gunthorpe wrote:
>>> On Thu, Jan 06, 2022 at 06:42:57AM +0000, lizhijian@...itsu.com wrote:
>>>> On 06/01/2022 08:28, Jason Gunthorpe wrote:
>>>>> On Tue, Dec 28, 2021 at 04:07:15PM +0800, Li Zhijian wrote:
>>>>>> +	while (length > 0) {
>>>>>> +		va	= (u8 *)(uintptr_t)buf->addr + offset;
>>>>>> +		bytes	= buf->size - offset;
>>>>>> +
>>>>>> +		if (bytes > length)
>>>>>> +			bytes = length;
>>>>>> +
>>>>>> +		arch_wb_cache_pmem(va, bytes);
>>>>> So why did we need to check that the va was pmem to call this?
>>>> Sorry, i didn't get you.
>>>>
>>>> I didn't check whether va is pmem, since only MR registered with PERSISTENCE(only pmem can
>>>> register this access flag) can reach here.
>>> Yes, that is what I mean,
>> I'm not sure I understand the *check* you mentioned above.
>>
>> Current code just dose something like:
>>
>> if (!sanity_check())
>>       return;
>> if (requested_plt == PERSISTENCE)
>>       va = iova_to_va(iova);
>>       arch_wb_cache_pmem(va, bytes);
>>       wmb;
>> else if (requested_plt == GLOBAL_VISIBILITY)
>>       wmb();
>>
>>
>>> why did we need to check anything to call
>>> this API
>> As above pseudo code,  it didn't *check* anything as what you said i think.
> I mean when you created the MR in the first place you checked for pmem
> before even allowing the persitent access flag.

Yes, that's true. that's because only pmem has ability to persist data.
So do you mean we don't need to prevent user to create/register a persistent
access flag to a non-pmem MR? it would be a bit confusing if so.


>
> Jason