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![]() - The biggest change is introduction of a new iteration of the SCHED_FAIR interactivity code: the EEVDF ("Earliest Eligible Virtual Deadline First") scheduler. EEVDF too is a virtual-time scheduler, with two parameters (weight and relative deadline), compared to CFS that had weight only. It completely reworks the base scheduler: placement, preemption, picking -- everything. LWN.net, as usual, has a terrific writeup about EEVDF: https://lwn.net/Articles/925371/ Preemption (both tick and wakeup) is driven by testing against a fresh pick. Because the tree is now effectively an interval tree, and the selection is no longer the 'leftmost' task, over-scheduling is less of a problem. A lot of the CFS heuristics are removed or replaced by more natural latency-space parameters & constructs. In terms of expected performance regressions: we'll and can fix everything where a 'good' workload misbehaves with the new scheduler, but EEVDF inevitably changes workload scheduling in a binary fashion, hopefully for the better in the overwhelming majority of cases, but in some cases it won't, especially in adversarial loads that got lucky with the previous code, such as some variants of hackbench. We are trying hard to err on the side of fixing all performance regressions, but we expect some inevitable post-release iterations of that process. - Improve load-balancing on hybrid x86 systems: enable cluster scheduling (again). - Improve & fix bandwidth-scheduling on nohz systems. - Improve bandwidth-throttling. - Use lock guards to simplify and de-goto-ify control flow. - Misc improvements, cleanups and fixes. Signed-off-by: Ingo Molnar <mingo@kernel.org> -----BEGIN PGP SIGNATURE----- iQJFBAABCgAvFiEEBpT5eoXrXCwVQwEKEnMQ0APhK1gFAmTtDOgRHG1pbmdvQGtl cm5lbC5vcmcACgkQEnMQ0APhK1iS4g//b9yewVW9OPxetKoN8zIJA0TjFYuuOVHK BlCJi5dbzXeCTrtENI65BRA7kPbTQ3AjwLRQ2BallAZ4dJceK0RhlZJvcrMNsm4e Adcpoch/FbqPKCrtAJQY04Ln1B244n/KyVifYett9220dMgTFQGJJYxrTc2G2+Kp F44vdUHzRczIE+KeOgBild1CwfKv5Zn5xgaXgtuoPLZtWBE0C1fSSzbK/PTINcUx bS4NVxK0CpOqSiNjnugV8KsYb71/0U6IgShBVjfHsrlBYigOH2NbVTH5xyjF8f83 WxiGstlhxj+N6Kv4L6FOJIAr2BIggH82j3FaPACmv4c8pzEoBBbvlAJkfinLEgbn Povg3OF2t6uZ8NoHjeu3WxOjBsphbpkFz7H5nno1ibXSIR/JyUH5MdBPSx93QITB QoUKQpr/L8zWauWDOEzSaJjEsZbl8rkcIVq5Bk0bR3qn2xkZsIeVte+vCEu3+tBc b4JOZjq7AuPDqPnsBLvuyiFZ7zwsAfm+pOD5UF3/zbLjPn1N/7wTNQZ29zjc04jl SifpCZGgF1KlG8m8wNTlSfVvq0ksppCzJt+C6VFuejZ191IGpirQHn4Vp0sluMhC WRzXhb7v37Bq5JY10GMfeKb/jAiRs68kozhzqVPsBSAPS6I6jJssONgedq+LbQdC tFsmE9n09do= =XtCD -----END PGP SIGNATURE----- Merge tag 'sched-core-2023-08-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip Pull scheduler updates from Ingo Molnar: - The biggest change is introduction of a new iteration of the SCHED_FAIR interactivity code: the EEVDF ("Earliest Eligible Virtual Deadline First") scheduler EEVDF too is a virtual-time scheduler, with two parameters (weight and relative deadline), compared to CFS that had weight only. It completely reworks the base scheduler: placement, preemption, picking -- everything LWN.net, as usual, has a terrific writeup about EEVDF: https://lwn.net/Articles/925371/ Preemption (both tick and wakeup) is driven by testing against a fresh pick. Because the tree is now effectively an interval tree, and the selection is no longer the 'leftmost' task, over-scheduling is less of a problem. A lot of the CFS heuristics are removed or replaced by more natural latency-space parameters & constructs In terms of expected performance regressions: we will and can fix everything where a 'good' workload misbehaves with the new scheduler, but EEVDF inevitably changes workload scheduling in a binary fashion, hopefully for the better in the overwhelming majority of cases, but in some cases it won't, especially in adversarial loads that got lucky with the previous code, such as some variants of hackbench. We are trying hard to err on the side of fixing all performance regressions, but we expect some inevitable post-release iterations of that process - Improve load-balancing on hybrid x86 systems: enable cluster scheduling (again) - Improve & fix bandwidth-scheduling on nohz systems - Improve bandwidth-throttling - Use lock guards to simplify and de-goto-ify control flow - Misc improvements, cleanups and fixes * tag 'sched-core-2023-08-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (43 commits) sched/eevdf/doc: Modify the documented knob to base_slice_ns as well sched/eevdf: Curb wakeup-preemption sched: Simplify sched_core_cpu_{starting,deactivate}() sched: Simplify try_steal_cookie() sched: Simplify sched_tick_remote() sched: Simplify sched_exec() sched: Simplify ttwu() sched: Simplify wake_up_if_idle() sched: Simplify: migrate_swap_stop() sched: Simplify sysctl_sched_uclamp_handler() sched: Simplify get_nohz_timer_target() sched/rt: sysctl_sched_rr_timeslice show default timeslice after reset sched/rt: Fix sysctl_sched_rr_timeslice intial value sched/fair: Block nohz tick_stop when cfs bandwidth in use sched, cgroup: Restore meaning to hierarchical_quota MAINTAINERS: Add Peter explicitly to the psi section sched/psi: Select KERNFS as needed sched/topology: Align group flags when removing degenerate domain sched/fair: remove util_est boosting sched/fair: Propagate enqueue flags into place_entity() ... |
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