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@xxxxxxxxxxxxxxx/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. -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
