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

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Message-ID: <20180320145626.GJ19744@ziepe.ca>
Date:   Tue, 20 Mar 2018 08:56:26 -0600
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Sinan Kaya <okaya@...eaurora.org>
Cc:     linux-rdma@...r.kernel.org, timur@...eaurora.org,
        sulrich@...eaurora.org, linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Faisal Latif <faisal.latif@...el.com>,
        Shiraz Saleem <shiraz.saleem@...el.com>,
        Doug Ledford <dledford@...hat.com>,
        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 10:47:45PM -0400, 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>
>  drivers/infiniband/hw/i40iw/i40iw_ctrl.c  |  6 ++++--
>  drivers/infiniband/hw/i40iw/i40iw_osdep.h |  1 +
>  drivers/infiniband/hw/i40iw/i40iw_uk.c    |  2 +-
>  drivers/infiniband/hw/i40iw/i40iw_utils.c | 11 +++++++++++
>  4 files changed, 17 insertions(+), 3 deletions(-)

The one looks fine

Reviewed-by: Jason Gunthorpe <jgg@...lanox.com>

Jason