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. + */ 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. > > 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, yet Jerin has acked that one and has explicitly > stated that he's OK with leaving CLDEMOTE as a noop on other architectures. > > -- > Thanks, > Anatoly
