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

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Message-ID: <20190712174525.GM27512@ziepe.ca>
Date:   Fri, 12 Jul 2019 14:45:25 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Bernard Metzler <BMT@...ich.ibm.com>
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: [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?

Jason