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One-Thread Active mode gives > > one PE the full core, while waking the other PE restores Two-Thread > > Active mode and partitions decode, issue, cache, TLB, and vector > > resources. Returning to full-resource mode requires the sibling to > > remain in WFI for 10 Ki cycles. > > > > Measurements show that pinned workloads perform equally on either PE, > > but freely migratable workloads lose substantial throughput when they > > alternate between PE identities. Consistently selecting PE0 keeps PE1 > > idle, avoids repeated SMT repartitioning, and restores > > one-thread-per-core performance. > > > > Describe this scheduling preference with SD_ASYM_PACKING and give PE0, > > identified by MPIDR_EL1.Aff0, the higher arch_asym_cpu_priority(). This > > is independent of SD_ASYM_CPUCAPACITY: SMT siblings retain equal > > capacity, while physical cores with different maximum frequencies are > > handled by a higher scheduling domain. > > > > Firmware currently provides no interface for describing the preferred > > SMT sibling. Detect Olympus by MIDR until such an interface is > > available. > > > > Signed-off-by: Andrea Righi > > Feel free to include: > > Reviewed-by: K Prateek Nayak > Tested-by: K Prateek Nayak > > Just one nit below ... > > +/* > > + * Switching the active PE on an NVIDIA Olympus SMT core can keep the core in > > + * two-thread active mode, with resources partitioned between the PEs. > > + * > > + * Prefer PE0 so PE1 can remain idle and the core can stay in full-resource > > + * mode. Firmware does not currently describe this preference, so detect > > + * Olympus by MIDR until a firmware interface is available. > > + */ > > +static bool olympus_prefer_pe0 __ro_after_init; > > nit. What is the purpose of "olympus_prefer_pe0"? > > > + > > +#ifdef CONFIG_SCHED_SMT > > +static int arm64_smt_flags(void) > > +{ > > + int flags = cpu_smt_flags(); > > + > > + if (olympus_prefer_pe0) > > + flags |= SD_ASYM_PACKING; > > If this flag function is being used, olympus_prefer_pe0 is always true, > and the scheduler will never call into arch_asym_cpu_priority() without > SD_ASYM_PACKING being set so olympus_prefer_pe0 is always true there > too. > > Seems redundant unless you were planning to do set_sched_topology() > unconditionally for whole of arm64. Right, there's no plan to install this topology unconditionally. Since arm64_asym_smt_topology is installed only after detecting an Olympus system with SMT, the boolean doesn't provide any additional state and can be removed. I'll do that in the next version. Thanks! -Andrea