kernel/include/linux/sched/topology.h, branch linux-6.18.y

sched/fair: Proportional newidle balance

2026-01-11T14:26:19Z

commit 33cf66d88306663d16e4759e9d24766b0aaa2e17 upstream. Add a randomized algorithm that runs newidle balancing proportional to its success rate. This improves schbench significantly: 6.18-rc4: 2.22 Mrps/s 6.18-rc4+revert: 2.04 Mrps/s 6.18-rc4+revert+random: 2.18 Mrps/S Conversely, per Adam Li this affects SpecJBB slightly, reducing it by 1%: 6.17: -6% 6.17+revert: 0% 6.17+revert+random: -1% Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Dietmar Eggemann Tested-by: Dietmar Eggemann Tested-by: Chris Mason Link: https://lkml.kernel.org/r/6825c50d-7fa7-45d8-9b81-c6e7e25738e2@meta.com Link: https://patch.msgid.link/20251107161739.770122091@infradead.org Signed-off-by: Greg Kroah-Hartman

sched: Move STDL_INIT() functions out-of-line

2025-09-03T08:03:13Z

Since all these functions are address-taken in SDTL_INIT() and called indirectly, it doesn't really make sense for them to be inline. Suggested-by: Christophe Leroy Signed-off-by: Peter Zijlstra (Intel)

sched/fair: Get rid of sched_domains_curr_level hack for tl->cpumask()

2025-09-03T08:03:12Z

Leon [1] and Vinicius [2] noted a topology_span_sane() warning during their testing starting from v6.16-rc1. Debug that followed pointed to the tl->mask() for the NODE domain being incorrectly resolved to that of the highest NUMA domain. tl->mask() for NODE is set to the sd_numa_mask() which depends on the global "sched_domains_curr_level" hack. "sched_domains_curr_level" is set to the "tl->numa_level" during tl traversal in build_sched_domains() calling sd_init() but was not reset before topology_span_sane(). Since "tl->numa_level" still reflected the old value from build_sched_domains(), topology_span_sane() for the NODE domain trips when the span of the last NUMA domain overlaps. Instead of replicating the "sched_domains_curr_level" hack, get rid of it entirely and instead, pass the entire "sched_domain_topology_level" object to tl->cpumask() function to prevent such mishap in the future. sd_numa_mask() now directly references "tl->numa_level" instead of relying on the global "sched_domains_curr_level" hack to index into sched_domains_numa_masks[]. The original warning was reproducible on the following NUMA topology reported by Leon: $ sudo numactl -H available: 5 nodes (0-4) node 0 cpus: 0 1 node 0 size: 2927 MB node 0 free: 1603 MB node 1 cpus: 2 3 node 1 size: 3023 MB node 1 free: 3008 MB node 2 cpus: 4 5 node 2 size: 3023 MB node 2 free: 3007 MB node 3 cpus: 6 7 node 3 size: 3023 MB node 3 free: 3002 MB node 4 cpus: 8 9 node 4 size: 3022 MB node 4 free: 2718 MB node distances: node 0 1 2 3 4 0: 10 39 38 37 36 1: 39 10 38 37 36 2: 38 38 10 37 36 3: 37 37 37 10 36 4: 36 36 36 36 10 The above topology can be mimicked using the following QEMU cmd that was used to reproduce the warning and test the fix: sudo qemu-system-x86_64 -enable-kvm -cpu host \ -m 20G -smp cpus=10,sockets=10 -machine q35 \ -object memory-backend-ram,size=4G,id=m0 \ -object memory-backend-ram,size=4G,id=m1 \ -object memory-backend-ram,size=4G,id=m2 \ -object memory-backend-ram,size=4G,id=m3 \ -object memory-backend-ram,size=4G,id=m4 \ -numa node,cpus=0-1,memdev=m0,nodeid=0 \ -numa node,cpus=2-3,memdev=m1,nodeid=1 \ -numa node,cpus=4-5,memdev=m2,nodeid=2 \ -numa node,cpus=6-7,memdev=m3,nodeid=3 \ -numa node,cpus=8-9,memdev=m4,nodeid=4 \ -numa dist,src=0,dst=1,val=39 \ -numa dist,src=0,dst=2,val=38 \ -numa dist,src=0,dst=3,val=37 \ -numa dist,src=0,dst=4,val=36 \ -numa dist,src=1,dst=0,val=39 \ -numa dist,src=1,dst=2,val=38 \ -numa dist,src=1,dst=3,val=37 \ -numa dist,src=1,dst=4,val=36 \ -numa dist,src=2,dst=0,val=38 \ -numa dist,src=2,dst=1,val=38 \ -numa dist,src=2,dst=3,val=37 \ -numa dist,src=2,dst=4,val=36 \ -numa dist,src=3,dst=0,val=37 \ -numa dist,src=3,dst=1,val=37 \ -numa dist,src=3,dst=2,val=37 \ -numa dist,src=3,dst=4,val=36 \ -numa dist,src=4,dst=0,val=36 \ -numa dist,src=4,dst=1,val=36 \ -numa dist,src=4,dst=2,val=36 \ -numa dist,src=4,dst=3,val=36 \ ... [ prateek: Moved common functions to include/linux/sched/topology.h, reuse the common bits for s390 and ppc, commit message ] Closes: https://lore.kernel.org/lkml/20250610110701.GA256154@unreal/ [1] Fixes: ccf74128d66c ("sched/topology: Assert non-NUMA topology masks don't (partially) overlap") # ce29a7da84cd, f55dac1dafb3 Signed-off-by: Peter Zijlstra (Intel) Reported-by: Leon Romanovsky Signed-off-by: K Prateek Nayak Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Valentin Schneider Reviewed-by: Shrikanth Hegde Tested-by: Valentin Schneider # x86 Tested-by: Shrikanth Hegde # powerpc Link: https://lore.kernel.org/lkml/a3de98387abad28592e6ab591f3ff6107fe01dc1.1755893468.git.tim.c.chen@linux.intel.com/ [2]

sched/topology: Remove sched_domain_topology_level::flags

2025-07-14T08:59:35Z

Support for overlapping domains added in commit e3589f6c81e4 ("sched: Allow for overlapping sched_domain spans") also allowed forcefully setting SD_OVERLAP for !NUMA domains via FORCE_SD_OVERLAP sched_feat(). Since NUMA domains had to be presumed overlapping to ensure correct behavior, "sched_domain_topology_level::flags" was introduced. NUMA domains added the SDTL_OVERLAP flag would ensure SD_OVERLAP was always added during build_sched_domains() for these domains, even when FORCE_SD_OVERLAP was off. Condition for adding the SD_OVERLAP flag at the aforementioned commit was as follows: if (tl->flags & SDTL_OVERLAP || sched_feat(FORCE_SD_OVERLAP)) sd->flags |= SD_OVERLAP; The FORCE_SD_OVERLAP debug feature was removed in commit af85596c74de ("sched/topology: Remove FORCE_SD_OVERLAP") which left the NUMA domains as the exclusive users of SDTL_OVERLAP, SD_OVERLAP, and SD_NUMA flags. Get rid of SDTL_OVERLAP and SD_OVERLAP as they have become redundant and instead rely on SD_NUMA to detect the only overlapping domain currently supported. Since SDTL_OVERLAP was the only user of "tl->flags", get rid of "sched_domain_topology_level::flags" too. Signed-off-by: K Prateek Nayak Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/ba4dbdf8-bc37-493d-b2e0-2efb00ea3e19@amd.com

smpboot: introduce SDTL_INIT() helper to tidy sched topology setup

2025-07-14T08:59:34Z

Define a small SDTL_INIT(maskfn, flagsfn, name) macro and use it to build the sched_domain_topology_level array. Purely a cleanup; behaviour is unchanged. Suggested-by: Thomas Gleixner Signed-off-by: Li Chen Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: K Prateek Nayak Tested-by: K Prateek Nayak Link: https://lore.kernel.org/r/20250710105715.66594-2-me@linux.beauty

sched/smp: Make SMP unconditional

2025-06-13T06:47:18Z

Simplify the scheduler by making CONFIG_SMP=y primitives and data structures unconditional. Introduce transitory wrappers for functionality not yet converted to SMP. Note that this patch is pretty large, because there's no clear separation between various aspects of the SMP scheduler, it's basically a huge block of #ifdef CONFIG_SMP. A fair amount of it has to be switched on for it to boot and work on UP systems. Signed-off-by: Ingo Molnar Acked-by: Peter Zijlstra Cc: Dietmar Eggemann Cc: Juri Lelli Cc: Linus Torvalds Cc: Mel Gorman Cc: Sebastian Andrzej Siewior Cc: Shrikanth Hegde Cc: Steven Rostedt Cc: Valentin Schneider Cc: Vincent Guittot Link: https://lore.kernel.org/r/20250528080924.2273858-21-mingo@kernel.org

sched/topology: Introduce sched_update_asym_prefer_cpu()

2025-04-16T19:09:11Z

A subset of AMD Processors supporting Preferred Core Rankings also feature the ability to dynamically switch these rankings at runtime to bias load balancing towards or away from the LLC domain with larger cache. To support dynamically updating "sg->asym_prefer_cpu" without needing to rebuild the sched domain, introduce sched_update_asym_prefer_cpu() which recomutes the "asym_prefer_cpu" when the core-ranking of a CPU changes. sched_update_asym_prefer_cpu() swaps the "sg->asym_prefer_cpu" with the CPU whose ranking has changed if the new ranking is greater than that of the "asym_prefer_cpu". If CPU whose ranking has changed is the current "asym_prefer_cpu", it scans the CPUs of the sched groups to find the new "asym_prefer_cpu" and sets it accordingly. get_group() for non-overlapping sched domains returns the sched group for the first CPU in the sched_group_span() which ensures all CPUs in the group see the updated value of "asym_prefer_cpu". Overlapping groups are allocated differently and will require moving the "asym_prefer_cpu" to "sg->sgc" but since the current implementations do not set "SD_ASYM_PACKING" at NUMA domains, skip additional indirection and place a SCHED_WARN_ON() to alert any future users. Signed-off-by: K Prateek Nayak Signed-off-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/r/20250409053446.23367-3-kprateek.nayak@amd.com

sched/debug: Make CONFIG_SCHED_DEBUG functionality unconditional

2025-03-19T21:20:53Z

All the big Linux distros enable CONFIG_SCHED_DEBUG, because the various features it provides help not just with kernel development, but with system administration and user-space software development as well. Reflect this reality and enable this functionality unconditionally. Signed-off-by: Ingo Molnar Tested-by: Shrikanth Hegde Cc: Peter Zijlstra Cc: Juri Lelli Cc: Vincent Guittot Cc: Dietmar Eggemann Cc: Steven Rostedt Cc: Ben Segall Cc: Mel Gorman Cc: Valentin Schneider Cc: Linus Torvalds Link: https://lore.kernel.org/r/20250317104257.3496611-4-mingo@kernel.org

include/{topology,cpuset}: Move dl_rebuild_rd_accounting to cpuset.h

2025-03-17T10:23:43Z

dl_rebuild_rd_accounting() is defined in cpuset.c, so it makes more sense to move related declarations to cpuset.h. Implement the move. Suggested-by: Waiman Long Signed-off-by: Juri Lelli Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Waiman Long Reviewed-by: Valentin Schneider Reviewed-by: Dietmar Eggemann Tested-by: Waiman Long Tested-by: Jon Hunter Tested-by: Dietmar Eggemann Link: https://lore.kernel.org/r/Z9MSOVMpU7jpVrMU@jlelli-thinkpadt14gen4.remote.csb

sched/topology: Stop exposing partition_sched_domains_locked

2025-03-17T10:23:43Z

The are no callers of partition_sched_domains_locked() outside topology.c. Stop exposing such function. Suggested-by: Waiman Long Signed-off-by: Juri Lelli Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Valentin Schneider Reviewed-by: Dietmar Eggemann Tested-by: Waiman Long Tested-by: Jon Hunter Tested-by: Dietmar Eggemann Link: https://lore.kernel.org/r/Z9MSC96a8FcqWV3G@jlelli-thinkpadt14gen4.remote.csb