On 13 June 2016 at 14:25, Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote: > On 13/06/16 11:58, Shawn Lin wrote: >> 在 2016/6/13 16:17, Adrian Hunter 写道: >>> On 13/06/16 10:48, Shawn Lin wrote: >>>> On 2016/6/13 14:29, Adrian Hunter wrote: >>>>> On 06/06/16 06:07, Shawn Lin wrote: >>>>>> JEDEC eMMC v5.1 introduce an autonomously initiated method >>>>>> for background operations. >>>>>> >>>>>> Host that wants to enable the device to perform background >>>>>> operations during device idle time, should signal the device >>>>>> by setting AUTO_EN in BKOPS_EN field EXT_CSD[163] to 1b. When >>>>>> this bit is set, the device may start or stop background operations >>>>>> whenever it sees fit, without any notification to the host. >>>>>> >>>>>> When AUTO_EN bit is set, the host should keep the device power >>>>>> active. The host may set or clear this bit at any time based on >>>>>> its power constraints or other considerations. >>>>>> >>>>>> Currently the manual bkops is only be used under the async req >>>>>> circumstances and it's a bit complicated to be controlled as the >>>>>> perfect method is that we should do some idle monitor just as rpm >>>>>> and send HPI each time if receiving rd/wr req. But it will impact >>>>>> performance significantly, especially for random iops since the >>>>>> weight of executing HPI against r/w small piece of LBAs is >>>>>> nonnegligible. >>>>>> >>>>>> So we now prefer to select the auto one unconditionally if supported >>>>>> which makes it as simple as possible. It should really good enough >>>>>> for devices to manage its internal policy for bkops rather than the >>>>>> host, which makes us believe that we could achieve the best >>>>>> performance for all the devices implementing auto bkops and the only >>>>>> thing we should do is to disable it when cutting off the power. >>>>> >>>>> Do you know if there is really a requirement to do that? >>>> >>>> Even without bkops enable, no matter for manual or auto one, FTL should >>>> always do bkops like GC internally when needed to guarantee the >>>> performance and balance the wear leveling. What I thought to do is to >>>> make it more explicitly. >>>> >>>> Because then, what >>>>> is the point of power off notification? >>>> >>>> When power off notification is sent, bkops will be stopped >>>> in _mmc_suspend. So I don't undertand your point here? >>> >>> I am trying to understand why we need to do anything for auto bkops. >>> Since AUTO_EN is persistent, we can leave the decision whether to turn it on >>> to whomever provisions the device. Then we just leave it alone. >>> >> >> Hrm.. >> >> one possible way is to control it by mmc-utils on >> user space? So we should add a cmd for mmc-utils >> there? > > That would be consistent with manual bkops. > >From my first impression I agree, as that is the policy we have been sticking to when writing to persistent EXT_CSD registers. Although, in this case, I am actually wondering on what is the best approach. Is there really ever a case when we don't want auto BKOPS to be default enabled? I think BKOPS is a fundamental feature of an FTL and I can't see a reason to why we need to involve mmc-utils/userspace to enable it. Am I wrong? Kind regards Uffe -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
