From: Beata Michalska <firstname.lastname@example.org> To: email@example.com Cc: firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com Subject: [RFC PATCH v2 0/3] Rework CPU capacity asymmetry detection Date: Wed, 28 Apr 2021 10:32:40 +0100 [thread overview] Message-ID: <firstname.lastname@example.org> (raw) As of now, the asym_cpu_capacity_level will try to locate the lowest topology level where the highest available CPU capacity is being visible to all CPUs. This works perfectly fine for most of existing asymmetric designs out there, though for some possible and completely valid setups, combining different cpu microarchitectures within clusters, this might not be the best approach, resulting in pointing at a level, at which some of the domains might not see any asymmetry at all. This could be problematic for misfit migration and/or energy aware placement. And as such, for affected platforms it might result in custom changes to wake-up and CPU selection paths. As mentioned in the previous version, based on the available sources out there, one of the potentially affected (by original approach) platforms might be Exynos 9820/990 with it's 'sliced' LLC divided between the two custom (big) cores and the remaining A75/A55 cores, which seems to be reflected in the made available dt entries for those platforms. The following patches rework how the asymmetric detection is being carried out, pinning the asymmetric topology level to the lowest one, where full range of CPU capacities is visible to all CPUs within given sched domain. The asym_cpu_capacity_level will also keep track of those levels where any scope of asymmetry is being observed, to denote corresponding sched domains with the SD_ASYM_CPUCAPACITY flag and to enable misfit migration for those. In order to distinguish the sched domains with partial vs full range of CPU capacity asymmetry, new sched domain flag has been introduced: SD_ASYM_CPUCAPACITY_FULL. The overall idea of changing the asymmetry detection has been suggested earlier by Valentin Schneider <email@example.com> Verified on (mostly): - QEMU (version 4.2.1) with variants of possible asymmetric topologies - machine: virt - modifying the device-tree 'cpus' node for virt machine: qemu-system-aarch64 -kernel $KERNEL_IMG -drive format=qcow2,file=$IMAGE -append 'root=/dev/vda earlycon console=ttyAMA0 sched_debug loglevel=15 kmemleak=on' -m 2G --nographic -cpu cortex-a57 -machine virt -smp cores=6 -machine dumpdtb=$CUSTOM_DTB.dtb $KERNEL_PATH/scripts/dtc/dtc -I dtb -O dts $CUSTOM_DTB.dts > $CUSTOM_DTB.dtb (modify the dts) $KERNEL_PATH/scripts/dtc/dtc -I dts -O dtb $CUSTOM_DTB.dts > $CUSTOM_DTB.dtb qemu-system-aarch64 -kernel $KERNEL_IMG -drive format=qcow2,file=$IMAGE -append 'root=/dev/vda earlycon console=ttyAMA0 sched_debug loglevel=15 kmemleak=on' -m 2G --nographic -cpu cortex-a57 -machine virt -smp cores=6 -machine dtb=$CUSTOM_DTB.dtb v2: - Fixed style issues - Reworked accessing the cached topology data as suggested by Valentin Beata Michalska (3): sched/core: Introduce SD_ASYM_CPUCAPACITY_FULL sched_domain flag sched/topology: Rework CPU capacity asymmetry detection sched/doc: Update the CPU capacity asymmetry bits Documentation/scheduler/sched-capacity.rst | 6 +- Documentation/scheduler/sched-energy.rst | 2 +- include/linux/sched/sd_flags.h | 10 + kernel/sched/topology.c | 327 +++++++++++++++++++++++++---- 4 files changed, 302 insertions(+), 43 deletions(-) -- 2.7.4
next reply other threads:[~2021-04-28 9:32 UTC|newest] Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-04-28 9:32 Beata Michalska [this message] 2021-04-28 9:32 ` [RFC PATCH v2 1/3] sched/core: Introduce SD_ASYM_CPUCAPACITY_FULL sched_domain flag Beata Michalska 2021-04-28 9:32 ` [RFC PATCH v2 2/3] sched/topology: Rework CPU capacity asymmetry detection Beata Michalska 2021-05-05 18:17 ` Valentin Schneider 2021-04-28 9:32 ` [RFC PATCH v2 3/3] sched/doc: Update the CPU capacity asymmetry bits Beata Michalska 2021-04-28 17:19 ` Randy Dunlap 2021-05-10 16:33 ` Beata Michalska 2021-05-05 18:17 ` [RFC PATCH v2 0/3] Rework CPU capacity asymmetry detection Valentin Schneider
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