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Load-balancing improvements: ============================ - Improve NUMA balancing on AMD Zen systems for affine workloads. - Improve the handling of reduced-capacity CPUs in load-balancing. - Energy Model improvements: fix & refine all the energy fairness metrics (PELT), and remove the conservative threshold requiring 6% energy savings to migrate a task. Doing this improves power efficiency for most workloads, and also increases the reliability of energy-efficiency scheduling. - Optimize/tweak select_idle_cpu() to spend (much) less time searching for an idle CPU on overloaded systems. There's reports of several milliseconds spent there on large systems with large workloads ... [ Since the search logic changed, there might be behavioral side effects. ] - Improve NUMA imbalance behavior. On certain systems with spare capacity, initial placement of tasks is non-deterministic, and such an artificial placement imbalance can persist for a long time, hurting (and sometimes helping) performance. The fix is to make fork-time task placement consistent with runtime NUMA balancing placement. Note that some performance regressions were reported against this, caused by workloads that are not memory bandwith limited, which benefit from the artificial locality of the placement bug(s). Mel Gorman's conclusion, with which we concur, was that consistency is better than random workload benefits from non-deterministic bugs: "Given there is no crystal ball and it's a tradeoff, I think it's better to be consistent and use similar logic at both fork time and runtime even if it doesn't have universal benefit." - Improve core scheduling by fixing a bug in sched_core_update_cookie() that caused unnecessary forced idling. - Improve wakeup-balancing by allowing same-LLC wakeup of idle CPUs for newly woken tasks. - Fix a newidle balancing bug that introduced unnecessary wakeup latencies. ABI improvements/fixes: ======================= - Do not check capabilities and do not issue capability check denial messages when a scheduler syscall doesn't require privileges. (Such as increasing niceness.) - Add forced-idle accounting to cgroups too. - Fix/improve the RSEQ ABI to not just silently accept unknown flags. (No existing tooling is known to have learned to rely on the previous behavior.) - Depreciate the (unused) RSEQ_CS_FLAG_NO_RESTART_ON_* flags. Optimizations: ============== - Optimize & simplify leaf_cfs_rq_list() - Micro-optimize set_nr_{and_not,if}_polling() via try_cmpxchg(). Misc fixes & cleanups: ====================== - Fix the RSEQ self-tests on RISC-V and Glibc 2.35 systems. - Fix a full-NOHZ bug that can in some cases result in the tick not being re-enabled when the last SCHED_RT task is gone from a runqueue but there's still SCHED_OTHER tasks around. - Various PREEMPT_RT related fixes. - Misc cleanups & smaller fixes. Signed-off-by: Ingo Molnar <mingo@kernel.org> -----BEGIN PGP SIGNATURE----- iQJFBAABCgAvFiEEBpT5eoXrXCwVQwEKEnMQ0APhK1gFAmLn2ywRHG1pbmdvQGtl cm5lbC5vcmcACgkQEnMQ0APhK1iNfxAAhPJMwM4tYCpIM6PhmxKiHl6kkiT2tt42 HhEmiJVLjczLybWaWwmGA2dSFkv1f4+hG7nqdZTm9QYn0Pqat2UTSRcwoKQc+gpB x85Hwt2IUmnUman52fRl5r1miH9LTdCI6agWaFLQae5ds1XmOugFo52t2ahax+Gn dB8LxS2fa/GrKj229EhkJSPWAK4Y94asoTProwpKLuKEeXhDkqUNrOWbKhz+wEnA pVZySpA9uEOdNLVSr1s0VB6mZoh5/z6yQefj5YSNntsG71XWo9jxKCIm5buVdk2U wjdn6UzoTThOy/5Ygm64eYRexMHG71UamF1JYUdmvDeUJZ5fhG6RD0FECUQNVcJB Msu2fce6u1AV0giZGYtiooLGSawB/+e6MoDkjTl8guFHi/peve9CezKX1ZgDWPfE eGn+EbYkUS9RMafXCKuEUBAC1UUqAavGN9sGGN1ufyR4za6ogZplOqAFKtTRTGnT /Ne3fHTtvv73DLGW9ohO5vSS2Rp7zhAhB6FunhibhxCWlt7W6hA4Ze2vU9hf78Yn SJDLAJjOEilLaKUkRG/d9uM3FjKJM1tqxuT76+sUbM0MNxdyiKcviQlP1b8oq5Um xE1KNZUevnr/WXqOTGDKHH/HNPFgwxbwavMiP7dNFn8h/hEk4t9dkf5siDmVHtn4 nzDVOob1LgE= =xr2b -----END PGP SIGNATURE----- Merge tag 'sched-core-2022-08-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip Pull scheduler updates from Ingo Molnar: "Load-balancing improvements: - Improve NUMA balancing on AMD Zen systems for affine workloads. - Improve the handling of reduced-capacity CPUs in load-balancing. - Energy Model improvements: fix & refine all the energy fairness metrics (PELT), and remove the conservative threshold requiring 6% energy savings to migrate a task. Doing this improves power efficiency for most workloads, and also increases the reliability of energy-efficiency scheduling. - Optimize/tweak select_idle_cpu() to spend (much) less time searching for an idle CPU on overloaded systems. There's reports of several milliseconds spent there on large systems with large workloads ... [ Since the search logic changed, there might be behavioral side effects. ] - Improve NUMA imbalance behavior. On certain systems with spare capacity, initial placement of tasks is non-deterministic, and such an artificial placement imbalance can persist for a long time, hurting (and sometimes helping) performance. The fix is to make fork-time task placement consistent with runtime NUMA balancing placement. Note that some performance regressions were reported against this, caused by workloads that are not memory bandwith limited, which benefit from the artificial locality of the placement bug(s). Mel Gorman's conclusion, with which we concur, was that consistency is better than random workload benefits from non-deterministic bugs: "Given there is no crystal ball and it's a tradeoff, I think it's better to be consistent and use similar logic at both fork time and runtime even if it doesn't have universal benefit." - Improve core scheduling by fixing a bug in sched_core_update_cookie() that caused unnecessary forced idling. - Improve wakeup-balancing by allowing same-LLC wakeup of idle CPUs for newly woken tasks. - Fix a newidle balancing bug that introduced unnecessary wakeup latencies. ABI improvements/fixes: - Do not check capabilities and do not issue capability check denial messages when a scheduler syscall doesn't require privileges. (Such as increasing niceness.) - Add forced-idle accounting to cgroups too. - Fix/improve the RSEQ ABI to not just silently accept unknown flags. (No existing tooling is known to have learned to rely on the previous behavior.) - Depreciate the (unused) RSEQ_CS_FLAG_NO_RESTART_ON_* flags. Optimizations: - Optimize & simplify leaf_cfs_rq_list() - Micro-optimize set_nr_{and_not,if}_polling() via try_cmpxchg(). Misc fixes & cleanups: - Fix the RSEQ self-tests on RISC-V and Glibc 2.35 systems. - Fix a full-NOHZ bug that can in some cases result in the tick not being re-enabled when the last SCHED_RT task is gone from a runqueue but there's still SCHED_OTHER tasks around. - Various PREEMPT_RT related fixes. - Misc cleanups & smaller fixes" * tag 'sched-core-2022-08-01' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (32 commits) rseq: Kill process when unknown flags are encountered in ABI structures rseq: Deprecate RSEQ_CS_FLAG_NO_RESTART_ON_* flags sched/core: Fix the bug that task won't enqueue into core tree when update cookie nohz/full, sched/rt: Fix missed tick-reenabling bug in dequeue_task_rt() sched/core: Always flush pending blk_plug sched/fair: fix case with reduced capacity CPU sched/core: Use try_cmpxchg in set_nr_{and_not,if}_polling sched/core: add forced idle accounting for cgroups sched/fair: Remove the energy margin in feec() sched/fair: Remove task_util from effective utilization in feec() sched/fair: Use the same cpumask per-PD throughout find_energy_efficient_cpu() sched/fair: Rename select_idle_mask to select_rq_mask sched, drivers: Remove max param from effective_cpu_util()/sched_cpu_util() sched/fair: Decay task PELT values during wakeup migration sched/fair: Provide u64 read for 32-bits arch helper sched/fair: Introduce SIS_UTIL to search idle CPU based on sum of util_avg sched: only perform capability check on privileged operation sched: Remove unused function group_first_cpu() sched/fair: Remove redundant word " *" selftests/rseq: check if libc rseq support is registered ... |
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