On Fri, Oct 09, 2020 at 12:12:56PM +0100, Burakov, Anatoly wrote: > On 09-Oct-20 11:48 AM, Ananyev, Konstantin wrote: > > > On 09-Oct-20 11:17 AM, Thomas Monjalon wrote: > > > > 09/10/2020 12:03, Burakov, Anatoly: > > > > > On 09-Oct-20 10:54 AM, Jerin Jacob wrote: > > > > > > On Fri, Oct 9, 2020 at 3:10 PM Burakov, Anatoly > > > > > > <anatoly.bura...@intel.com> wrote: > > > > > > > On 09-Oct-20 10:29 AM, Thomas Monjalon wrote: > > > > > > > > 09/10/2020 11:25, Burakov, Anatoly: > > > > > > > > > On 09-Oct-20 6:42 AM, Jerin Jacob wrote: > > > > > > > > > > On Thu, Oct 8, 2020 at 10:38 PM Ananyev, Konstantin > > > > > > > > > > <konstantin.anan...@intel.com> wrote: > > > > > > > > > > > > On Thu, Oct 8, 2020 at 6:57 PM Burakov, Anatoly > > > > > > > > > > > > <anatoly.bura...@intel.com> wrote: > > > > > > > > > > > > > On 08-Oct-20 9:44 AM, Jerin Jacob wrote: > > > > > > > > > > > > > > On Thu, Oct 8, 2020 at 2:04 PM Thomas Monjalon > > > > > > > > > > > > > > <tho...@monjalon.net> wrote: > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Add two new power management intrinsics, and > > > > > > > > > > > > > > > > provide an implementation > > > > > > > > > > > > > > > > in eal/x86 based on UMONITOR/UMWAIT > > > > > > > > > > > > > > > > instructions. The instructions > > > > > > > > > > > > > > > > are implemented as raw byte opcodes because > > > > > > > > > > > > > > > > there is not yet widespread > > > > > > > > > > > > > > > > compiler support for these instructions. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > The power management instructions provide an > > > > > > > > > > > > > > > > architecture-specific > > > > > > > > > > > > > > > > function to either wait until a specified TSC > > > > > > > > > > > > > > > > timestamp is reached, or > > > > > > > > > > > > > > > > optionally wait until either a TSC timestamp is > > > > > > > > > > > > > > > > reached or a memory > > > > > > > > > > > > > > > > location is written to. The monitor function > > > > > > > > > > > > > > > > also provides an optional > > > > > > > > > > > > > > > > comparison, to avoid sleeping when the expected > > > > > > > > > > > > > > > > write has already > > > > > > > > > > > > > > > > happened, and no more writes are expected. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > For more details, Please reference Intel SDM > > > > > > > > > > > > > > > > Volume 2. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > I really would like to see feedbacks from other > > > > > > > > > > > > > > > arch maintainers. > > > > > > > > > > > > > > > Unfortunately they were not Cc'ed. > > > > > > > > > > > > > > > > > > > > > > > > > > > > Shared the feedback from the arm64 perspective > > > > > > > > > > > > > > here. Yet to get a reply on this. > > > > > > > > > > > > > > http://mails.dpdk.org/archives/dev/2020-September/181646.html > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Also please mark the new functions as > > > > > > > > > > > > > > > experimental. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Hi Jerin, > > > > > > > > > > > > > > > > > > > > > > > > Hi Anatoly, > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > IMO, We must introduce some arch > > > > > > > > > > > > > feature-capability _get_ scheme to tell > > > > > > > > > > > > > > the consumer of this API is only supported on > > > > > > > > > > > > > x86. Probably as > > > > > > > > > > > > > functions[1] > > > > > > > > > > > > > > or macro flags scheme and have a stub for the > > > > > > > > > > > > > other architectures as the > > > > > > > > > > > > > > API marked as generic ie rte_power_* not > > > > > > > > > > > > > rte_x86_.. > > > > > > > > > > > > > > > > > > > > > > > > > > > > This will help the consumer to create workers > > > > > > > > > > > > > based on the > > > > > > > > > > > > > instruction features > > > > > > > > > > > > > > which can NOT be abstracted as a generic > > > > > > > > > > > > > feature across the > > > > > > > > > > > > > architectures. > > > > > > > > > > > > > > > > > > > > > > > > > > I'm not entirely sure what you mean by that. > > > > > > > > > > > > > > > > > > > > > > > > > > I mean, yes, we should have added stubs for other > > > > > > > > > > > > > architectures, and we > > > > > > > > > > > > > will add those in future revisions, but what does > > > > > > > > > > > > > your proposed runtime > > > > > > > > > > > > > check accomplish that cannot currently be done with > > > > > > > > > > > > > CPUID flags? > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > RTE_CPUFLAG_WAITPKG flag definition is not available > > > > > > > > > > > > in other architectures. > > > > > > > > > > > > i.e RTE_CPUFLAG_WAITPKG defined in > > > > > > > > > > > > lib/librte_eal/x86/include/rte_cpuflags.h > > > > > > > > > > > > and it is used in http://patches.dpdk.org/patch/79540/ > > > > > > > > > > > > as generic API. > > > > > > > > > > > > I doubt http://patches.dpdk.org/patch/79540/ would > > > > > > > > > > > > compile on non-x86. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > I am agree with Jerin, that we need some generic way to > > > > > > > > > > > figure-out does platform supports power_monitor() or not. > > > > > > > > > > > Though not sure do we need to create a new feature-get > > > > > > > > > > > framework here... > > > > > > > > > > > > > > > > > > > > That's works too. Some means of generic probing is fine. > > > > > > > > > > Following > > > > > > > > > > schemed needs > > > > > > > > > > more documentation on that usage, as, it is not straight > > > > > > > > > > forward compare to > > > > > > > > > > feature-get framework. Also, on the other thread, we are > > > > > > > > > > adding the > > > > > > > > > > new instructions like > > > > > > > > > > demote cacheline etc, maybe if the user wants to KNOW if > > > > > > > > > > the arch > > > > > > > > > > supports it then > > > > > > > > > > the feature-get framework is good. > > > > > > > > > > If we think, there is no other usecase for generic arch > > > > > > > > > > feature-get > > > > > > > > > > framework then > > > > > > > > > > we can keep the below scheme else generic arch feature is > > > > > > > > > > better for > > > > > > > > > > more forward > > > > > > > > > > looking use cases. > > > > > > > > > > > > > > > > > > > > > Might be just something like: > > > > > > > > > > > rte_power_monitor(...) == -ENOTSUP > > > > > > > > > > > be enough indication for that? > > > > > > > > > > > So user can just do: > > > > > > > > > > > if (rte_power_monitor(NULL, 0, 0, 0, 0) == -ENOTSUP) { > > > > > > > > > > > /* not supported path */ > > > > > > > > > > > } > > > > > > > > > > > > > > > > > > > > > > To check is that feature supported or not. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > Looking at CLDEMOTE patches, CLDEMOTE is a noop on other > > > > > > > > > archs. I think > > > > > > > > > we can safely make this intrinsic as a noop on other archs as > > > > > > > > > well, as > > > > > > > > > it's functionally identical to waking up immediately. > > > > > > > > > > > > > > > > > > If we're not creating this for CLDEMOTE, we don't need it > > > > > > > > > here as well. > > > > > > > > > If we do need it for this, then we arguably need it for > > > > > > > > > CLDEMOTE too. > > > > > > > > > > > > > > > > Sorry I don't understand what you mean, too many "it" and > > > > > > > > "this" :) > > > > > > > > > > > > > > > > > > > > > > Sorry, i meant "the generic feature-get framework". CLDEMOTE > > > > > > > doesn't > > > > > > > exist on other archs, this doesn't too, so it's a fairly similar > > > > > > > situation. Stubbing UMWAIT with a noop is a valid approach > > > > > > > because it's > > > > > > > equivalent to sleeping and then immediately waking up (which can > > > > > > > happen > > > > > > > for a host of reasons unrelated to the code itself). > > > > > > > > > > > > If we are keeping the following return in the public API then it > > > > > > can not be NOP > > > > > > + * @return > > > > > > + * - 1 if wakeup was due to TSC timeout expiration. > > > > > > + * - 0 if wakeup was due to memory write or other reasons. > > > > > > + */ > > > > > > > > > > > > > > > > In the generic header, it is specified that return value is > > > > > implementation-defined (i.e. arch-specific). > > > > > > > > Obviously an API definition should *never* be "implementation-defined". > > > > > > If there isn't a meaningful return value, we could either make it a > > > void, or return 0/-ENOTSUP so. I'm OK with either as nop is a valid > > > result for a UMWAIT, and there are no side-effects to the intrinsic > > > itself (it's basically a fancy rte_pause). > > > > > > > > > > > > > > > > I guess we could remove > > > > > that and set return value to either 0 or -ENOTSUP if that would > > > > > resolve > > > > > the issue? > > > > > > > > > > > Also, we need to fix compilation issue if any with > > > > > > http://patches.dpdk.org/patch/79540/ > > > > > > as it has direct reference to if > > > > > > (!rte_cpu_get_flag_enabled(RTE_CPUFLAG_WAITPKG)) { > > > > > > Either we need to add -ENOTSUP return or generic feature-get > > > > > > framework. > > > > > > > > > > IIRC power library isn't compiled on anything other than x86, so this > > > > > code wouldn't get compiled. > > > > > > > > It is not call "power-x86", so we must assume it could work > > > > on any architecture. > > > > > > #ifdef it is! > > > > > > > > > > > > > > > > > > I'm not against a generic feature-get framework, i'm just > > > > > > > pointing out > > > > > > > that if this is what's preventing the merge, it should prevent > > > > > > > the merge > > > > > > > of CLDEMOTE as well > > > > I wouldn't consider these two as totally equal. > > Yes, both are just hints to CPU, that can be ignored, > > but if not, then consequences of executing are quite different. > > If UMWAIT is not supported by cpu at all, then user might want to use some > > different power saving mechanism (pause, frequence scaling, etc.). > > Without information is UMWAIT supported or not, user can't make > > such choice. > > After some attempts at implementing this, i actually came to the conclusion > that some generic way to check support for this feature is necessary, > because we end up with a usability inconsistency: > > 1) on non-x86, if you call the function, it returns -ENOTSUP > 2) on x86, since we're not checking CPUID flags on every single call, it'll > either succeed, or crash the process - the burden is on the user to check > for CPUID flags, but it can't be done in an arch agnostic way because the > CPUID flags are only defined for x86, thus requiring a special code path for > x86 > > Where would be the best place to add such an infrastructure? I'm thinking > rte_cpuflags.h? > Time to relook at some of the contents of patchset: http://patches.dpdk.org/project/dpdk/list/?series=4811&archive=both&state=*
The idea of that set (IIRC) was to replace the per-architecture enums with just strings to avoid situations like this - or at least make them less awkward. /Bruce
