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 and posted this series. Note also that I have one Infiniband patch in the 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. Changes since v1: i40e/i40evf: Eliminate duplicate barriers on weakly-ordered archs missed writel calls in: i40e: i40e_program_fdir_filter i40e_clean_rx_irq i40e_tx_map i40evf: i40e_clean_rx_irq i40e_tx_map ixgbe: eliminate duplicate barriers on weakly-ordered archs missed the writel at the end of ixgbe_tx_map RDMA/qedr: eliminate duplicate barriers on weakly-ordered archs dropped since applied igbvf: eliminate duplicate barriers on weakly-ordered archs missed the writel at the end of igbvf_tx_queue_adv() igb: eliminate duplicate barriers on weakly-ordered archs missed the writel at the end of igb_tx_map() e1000: eliminate duplicate barriers on weakly-ordered archs dropped ixgbevf: eliminate duplicate barriers on weakly-ordered archs split into two and remove extra barrier. Sinan Kaya (6): 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 ixgbevf: keep writel() closer to wmb() ixgbevf: eliminate duplicate barriers on weakly-ordered archs drivers/net/ethernet/intel/i40e/i40e_txrx.c | 8 ++++---- 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 | 4 ++-- 7 files changed, 16 insertions(+), 21 deletions(-) -- 2.7.4 -- 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
