On 2018-03-23 19:58, Jeff Kirsher wrote:
On Fri, 2018-03-23 at 14:53 -0700, Alexander Duyck wrote:
On Fri, Mar 23, 2018 at 11:52 AM, Sinan Kaya <okaya@xxxxxxxxxxxxxx>
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@xxxxxxxxx>
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.
Sorry, you will have to replace the ones you took from me.
>
> 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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