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

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Message-ID: <CAKgT0UcaxM8Mj9Y9fR0B+aafTm1SzTqh+gHT5ozgvyaoHvrzRQ@mail.gmail.com>
Date:   Fri, 23 Mar 2018 14:53:04 -0700
From:   Alexander Duyck <alexander.duyck@...il.com>
To:     Sinan Kaya <okaya@...eaurora.org>,
        intel-wired-lan <intel-wired-lan@...ts.osuosl.org>
Cc:     Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
        Netdev <netdev@...r.kernel.org>,
        Timur Tabi <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: intel: Eliminate duplicate barriers on
 weakly-ordered archs

On Fri, Mar 23, 2018 at 11:52 AM, Sinan Kaya <okaya@...eaurora.org> wrote:
> 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.

I looked over the set and they seem good.

Reviewed-by: Alexander Duyck <alexander.h.duyck@...el.com>

>
> Changes since v6:
> clean up between 2..6 and then make your Alex's changes on 1 and 7
>     The mmiowb shouldn't be needed for Rx. Only one CPU will be running
>     NAPI for the queue and we will synchronize this with a full writel
>     anyway when we re-enable the interrupts.
>
> Sinan Kaya (7):
>   i40e/i40evf: Eliminate duplicate barriers on weakly-ordered archs
>   ixgbe: eliminate duplicate barriers on weakly-ordered archs
>   igbvf: eliminate duplicate barriers on weakly-ordered archs
>   igb: eliminate duplicate barriers on weakly-ordered archs
>   fm10k: Eliminate duplicate barriers on weakly-ordered archs
>   ixgbevf: keep writel() closer to wmb()
>   ixgbevf: eliminate duplicate barriers on weakly-ordered archs
>
>  drivers/net/ethernet/intel/fm10k/fm10k_main.c     |  4 ++--
>  drivers/net/ethernet/intel/i40e/i40e_txrx.c       | 14 ++++++++++----
>  drivers/net/ethernet/intel/i40evf/i40e_txrx.c     |  4 ++--
>  drivers/net/ethernet/intel/igb/igb_main.c         |  4 ++--
>  drivers/net/ethernet/intel/igbvf/netdev.c         |  4 ++--
>  drivers/net/ethernet/intel/ixgbe/ixgbe_main.c     |  8 ++++----
>  drivers/net/ethernet/intel/ixgbevf/ixgbevf.h      |  5 -----
>  drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c | 11 ++++++++---
>  8 files changed, 30 insertions(+), 24 deletions(-)
>
> --
> 2.7.4
>