netdev - Re: [PATCH v8 0/7] netdev: intel: Eliminate duplicate barriers on weakly-ordered archs

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Date:   Mon, 2 Apr 2018 22:59:13 -0400
From:   Sinan Kaya <okaya@...eaurora.org>
To:     jeffrey.t.kirsher@...el.com,
        Alexander Duyck <alexander.duyck@...il.com>
Cc:     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 v8 0/7] netdev: intel: Eliminate duplicate barriers on
 weakly-ordered archs

Alex,

On 4/2/2018 3:06 PM, Sinan Kaya 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.
> 
> Change since 7:
> 
> * API clarification with Linus and several architecture folks regarding
> writel()
> 
> https://www.mail-archive.com/netdev@vger.kernel.org/msg225806.html
> 
> * removed wmb() in front of writel() at several places.
> * remove old IA64 comments regarding ordering.
> 

What do you think about this version? Did I miss any SMP barriers?


> 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     | 15 ++-----------
>  drivers/net/ethernet/intel/i40e/i40e_txrx.c       | 22 ++++++++----------
>  drivers/net/ethernet/intel/i40evf/i40e_txrx.c     |  8 +------
>  drivers/net/ethernet/intel/igb/igb_main.c         | 14 ++----------
>  drivers/net/ethernet/intel/igbvf/netdev.c         | 16 +++++---------
>  drivers/net/ethernet/intel/ixgbe/ixgbe_main.c     | 23 ++-----------------
>  drivers/net/ethernet/intel/ixgbevf/ixgbevf.h      |  5 -----
>  drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c | 27 ++++++++---------------
>  8 files changed, 30 insertions(+), 100 deletions(-)
> 

Sinan

-- 
Sinan Kaya
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.