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. Sure. -- Regards, Sudeep -- 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
