On 3/27/2018 12:54 PM, Jeff Kirsher wrote: > On Tue, 2018-03-27 at 08:42 -0400, Sinan Kaya wrote: >> On 3/23/2018 10:34 PM, okaya@xxxxxxxxxxxxxx wrote: >>> 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@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@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. >> >> Double sorry now. >> >> 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 V8 or is it >> too late? > > Currently I do not have any of your patches applied to my next-queue > tree (dev-queue branch). So feel free to do any revisions you need to > do and to re-submit to intel-wired-lan@xxxxxxxxxxxxxxxx (IWL) mailing > list. > Thanks, Good to know. I'm waiting for the discussion to settle. I'll update as soon as I get a clear direction. -- 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
