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

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Date:   Mon, 10 Jan 2022 10:34:19 -0400
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     "lizhijian@...itsu.com" <lizhijian@...itsu.com>
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 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.

Jason