netdev - Re: [PATCH v7 0/7] netdev: Eliminate duplicate barriers on weakly-ordered archs

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Message-Id: <20180326.124846.2182144342929084561.davem@davemloft.net>
Date:   Mon, 26 Mar 2018 12:48:46 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     okaya@...eaurora.org
Cc:     netdev@...r.kernel.org, timur@...eaurora.org,
        sulrich@...eaurora.org, linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v7 0/7] netdev: Eliminate duplicate barriers on
 weakly-ordered archs

From: Sinan Kaya <okaya@...eaurora.org>
Date: Sun, 25 Mar 2018 10:39:14 -0400

> Code includes wmb() followed by writel() in multiple places. 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.
> 
> Since code already has an explicit barrier call, changing writel() to
> writel_relaxed().
> 
> I did a regex search for wmb() followed by writel() in each drivers
> directory.
> I scrubbed the ones I care about in this series.
> 
> I considered "ease of change", "popular usage" and "performance critical
> path" as the determining criteria for my filtering.
> 
> We used relaxed API heavily on ARM for a long time but
> it did not exist on other architectures. For this reason, relaxed
> architectures have been paying double penalty in order to use the common
> drivers.
> 
> Now that relaxed API is present on all architectures, we can go and scrub
> all drivers to see what needs to change and what can remain.
> 
> We start with mostly used ones and hope to increase the coverage over time.
> It will take a while to cover all drivers.
> 
> Feel free to apply patches individually.
> 
> Changes since v6:
> - bring back amazon ena and add mmiowb, remove
>   ena_com_write_sq_doorbell_rel(). 
> - remove extra mmiowb in bnx2x
> - correct spelling mistake in  bnx2x: Replace doorbell barrier() with wmb()

Series applied, thank you.