Hi Rafael, On 8/1/2017 11:34 AM, Sudeep Holla wrote: > > On 01/08/17 18:15, Prakash, Prashanth wrote: >> On 8/1/2017 3:18 AM, Sudeep Holla wrote: >>> On 31/07/17 19:18, Prakash, Prashanth wrote: >>>> Hi Sudeep, >>>> >>>> On 7/31/2017 10:25 AM, Sudeep Holla wrote: >>>>> Sorry for the delay, I initial thought having this ABI under testing is >>>>> fine as I really don't want any *real* user space programs to depend on >>>>> this for various reasons stated in earlier threads, e.g. h/w auto >>>>> promotable states, accuracy of the stats, ..etc >>>> <sorry for repeating this part> >>>> These fields are optional, so if there is no reliable way to keep track of stats, platform >>>> can choose not to expose it. If a platform is exposing inaccurate stats via this ACPI >>>> interface, it is breaking the spec. >>> Fair enough. >>> >>>>> But from Documentation/ABI/README, I see >>>>> >>>>> testing/ >>>>> This directory documents interfaces that are felt to be stable, >>>>> as the main development of this interface has been completed. >>>>> The interface can be changed to add new features, but the >>>>> current interface will not break by doing this, unless grave >>>>> errors or security problems are found in them. User space >>>>> programs can start to rely on these interfaces,... >>>>> >>>>> which makes me worry. Since the use for this is purely for debug or >>>>> optimization purposes, I still prefer simple single file debugfs entry. >>>>> I still can't digest the fact that reading single file is time consuming >>>>> as we are not using this interface at runtime IIUC. i.e. statistic are >>>>> collected and analyzed offline.>> These fields has the same utility/use-cases as the usage & time >>> fields in cpuidle sysfs, >>>> but provides more granularity - idle stats for different levels hierarchy and accurate >>>> idle stats for states that require platform co-ordination. >>>> >>> I completely agree with that and that's not the argument. >>> >>>> The argument for having a single sysfs file per node was that reading individual >>>> files might get expensive to get a snapshot(not the other way around). But, that >>>> argument was weak as we typically read these only in debug settings and not that >>>> often during runtime. So, the summary_stats file was removed and went with one >>>> value per file. >>>> >>> You are contradicting yourself above :). You say the argument you made >>> is weak :) but still went ahead and dropped single debugfs file vs the >>> standard per entry sysfs file which is an ABI. >> To clarify, the first RFC patch had a sysfs entry called summary_stats which >> provided all the stats for a specific node in hierarchy via a single file. The >> argument for having such a single file was weak. :) There was never a >> debugfs file to be dropped in first place. >> > You are right, it was me who keep suggesting debugfs file as a > replacement for your summary_stats sysfs file. Sorry for the confusion > but I still insist debugfs :) > >>> Since we already have CPUIdle sysfs which is an ABI, I am really not >>> sure if we need another set of ABI files which are used only for debug >>> and optimization purposes. Why is single debugfs file not sufficient ? >>> >> The consumers for this data are not all kernel developers. We will have other >> engineers looking at this data for power/performance optimizations and >> would be nice to give them a consistent interface. > Yes that's the case with any sysfs file users and that's why we can't > break ABI once we expose. > >>> As hardware evolves, most of the platforms can't provide these >>> information accurately. So if we are trying to address a problem which >>> is short-lived and on very small class of platforms, I would avoid >>> creating a new ABI for it. That's my main argument against this >>> interface instead go with debugfs entry. That's my opinion though. >> I would like to think of it in terms of ACPI spec rather than a subset of platforms. >> If it is part of spec there should be no reason to speculate on which platform >> may or may not implement it. We implement to the spec and ideally platform >> designers should ideally do the same. > >> Since sysfs vs debugfs is quite debatable :) , I will wait for Rafael's inputs. Any inputs on this? -- Thanks, Prashanth -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
