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

[Jeff Kirsher <jeffrey.t.kirsher@intel.com>]

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On Fri, 2018-03-23 at 14:53 -0700, Alexander Duyck wrote:
> On Fri, Mar 23, 2018 at 11:52 AM, Sinan Kaya <okaya@codeaurora.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@intel.com>

Grrr, patch 1 does not apply cleanly to my next-queue tree (dev-queue
branch).  I will deal with this series in a day or two, after I have dealt
with my driver pull requests.

> > 
> > 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
> > 

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