linux-kernel - Re: Re: Re: Re: Re: Re: [PATCH] rdma/siw: avoid smp_store

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Date:   Fri, 12 Jul 2019 18:06:22 +0000
From:   "Bernard Metzler" <BMT@...ich.ibm.com>
To:     "Jason Gunthorpe" <jgg@...pe.ca>
Cc:     "Arnd Bergmann" <arnd@...db.de>,
        "Doug Ledford" <dledford@...hat.com>,
        "Peter Zijlstra" <peterz@...radead.org>,
        linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re:  Re: Re: Re: Re: Re: [PATCH] rdma/siw: avoid smp_store_mb() on a u64

-----"Jason Gunthorpe" <jgg@...pe.ca> wrote: -----

>To: "Bernard Metzler" <BMT@...ich.ibm.com>
>From: "Jason Gunthorpe" <jgg@...pe.ca>
>Date: 07/12/2019 07:45PM
>Cc: "Arnd Bergmann" <arnd@...db.de>, "Doug Ledford"
><dledford@...hat.com>, "Peter Zijlstra" <peterz@...radead.org>,
>linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org
>Subject: [EXTERNAL] Re: Re: Re: Re: Re: [PATCH] rdma/siw: avoid
>smp_store_mb() on a u64
>
>On Fri, Jul 12, 2019 at 05:40:43PM +0000, Bernard Metzler wrote:
> 
>> It is because there are two levels a CQ can be armed:
>> 
>>        #include <infiniband/verbs.h>
>> 
>>        int ibv_req_notify_cq(struct ibv_cq *cq, int
>solicited_only);
>> 
>> If we kick the CQ handler, we have to clear the whole
>> thing. The user later again decides how he wants to get it
>> re-armed...SOLICITED completions only, or ALL signaled.
>
>Arrange it so only one of the two bits is ever set and do two
>test-and-set bits when a SOLICITED CQE comes in?
>
right, but that's too easy ;)
I'll probably do it along those lines.



Many thanks,
Bernard.