Dave, On 3/26/2018 12:48 PM, David Miller wrote: > From: Sinan Kaya <okaya@xxxxxxxxxxxxxx> > Date: Sun, 25 Mar 2018 10:39:14 -0400 > >> 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. >> >> Changes since v6: >> - bring back amazon ena and add mmiowb, remove >> ena_com_write_sq_doorbell_rel(). >> - remove extra mmiowb in bnx2x >> - correct spelling mistake in bnx2x: Replace doorbell barrier() with wmb() > > Series applied, thank you. > I don't know if you have been following "RFC on writel and writel_relaxed" thread or not but there are some new developments about wmb() requirement. Basically, wmb() should never be used before writel() as writel() seem to provide coherency and observability guarantee. wmb()+writel_relaxed() is slower on some architectures than plain writel() I'll have to rework these patches to have writel() only. Are you able to drop the applied ones so that I can post V7 or is it too late? 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
