linux-kernel - Re: [PATCH v4 3/6] RDMA/i40iw: Eliminate duplicate barriers on weakly-ordered archs

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Date:   Wed, 21 Mar 2018 08:38:06 -0500
From:   Shiraz Saleem <shiraz.saleem@...el.com>
To:     Sinan Kaya <okaya@...eaurora.org>
Cc:     "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        "timur@...eaurora.org" <timur@...eaurora.org>,
        "sulrich@...eaurora.org" <sulrich@...eaurora.org>,
        "linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "Latif, Faisal" <faisal.latif@...el.com>,
        Doug Ledford <dledford@...hat.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 3/6] RDMA/i40iw: Eliminate duplicate barriers on
 weakly-ordered archs

On Mon, Mar 19, 2018 at 08:47:45PM -0600, Sinan Kaya wrote:
> Code includes wmb() followed by writel(). writel() already has a barrier on
> some architectures like arm64.
> 
> This ends up CPU observing two barriers back to back before executing the
> register write.
> 
> Create a new wrapper function with relaxed write operator. Use the new
> wrapper when a write is following a wmb().
> 
> Since code already has an explicit barrier call, changing writel() to
> writel_relaxed().
> 
> Signed-off-by: Sinan Kaya <okaya@...eaurora.org>

Acked-by: Shiraz Saleem <shiraz.saleem@...el.com>