Messages in this thread | | | From | Patrick Bellasi <> | Subject | [PATCH v6 0/4] Utilization estimation (util_est) for FAIR tasks | Date | Fri, 9 Mar 2018 09:52:41 +0000 |
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Hi, here is an update of [1], based on today's tip/sched/core [2], which mainly adds some code cleanups suggested by Peter as well as fixes compilation for !CONFIG_SMP systems.
Most notably: a) The util_est's update flag has been renamed into UTIL_AVG_UNCHANGED, which seems to better match its usages. b) The cpu_util_est() function has been removed to reduce cluttering by folding its code directly into cpu_util(). This last function is thus now always returning the estimated utilization of a CPU, unless this sched feature is disabled. c) Not necessary READ_ONCE() have been removed from rq-lock protected code paths. For util_est variable, that we read/modify/write only from rq-lock protected, code we keep just the WRITE_ONCE() barriers, which are still required for synchronization with lockless readers. The READ_ONCE() have been instead maintained in all the getter functions, like for example task_util() and cpu_util(), which can potentially be used by lockless code. e.g. schedutil or load-balancer.
Results on both x86_64 and ARM (Android) targets, which have been collected and reported in previous postings [1,3], show negligible overheads, especially compared to the corresponding power/performance benefits on mobile platforms, where this feature helps to reduce the performance gap between PELT and another other out-of-tree load tracking solution.
Best, Patrick
.:: Changelog =============
Changes in v6: - remove READ_ONCE from rq-lock protected code paths - folds cpu_util_est code into cpu_util and update its documentation - change util_est's update flag name to better match its usage - slightly clean up cpu_util_wake code - add other small code cleanups as suggested by Peter - fix compilation for !CONFIG_SMP systems - fix documentation to match sphinx syntax - update changelogs to better match code concepts
Changes in v5: - rebased on today's tip/sched/core (commit 083c6eeab2cc, based on v4.16-rc2) - update util_est only on util_avg updates - add documentation for "struct util_est" - always use int instead of long whenever possible (Peter) - pass cfs_rq to util_est_{en,de}queue (Peter) - pass task_sleep to util_est_dequeue - use singe WRITE_ONCE at dequeue time - add some missing {READ,WRITE}_ONCE - add task_util_est() for code consistency
Changes in v4: - rebased on today's tip/sched/core (commit 460e8c3340a2) - renamed util_est's "last" into "enqueued" - using util_est's "enqueued" for both se and cfs_rqs (Joel) - update margin check to use more ASM friendly code (Peter) - optimize EWMA updates (Peter) - ensure cpu_util_wake() is cpu_capacity_orig()'s clamped (Pavan) - simplify cpu_util_cfs() integration (Dietmar)
Changes in v3: - rebased on today's tip/sched/core (commit 07881166a892) - moved util_est into sched_avg (Peter) - use {READ,WRITE}_ONCE() for EWMA updates (Peter) - using unsigned int to fit all sched_avg into a single 64B cache line - schedutil integration using Juri's cpu_util_cfs() - first patch dropped since it's already queued in tip/sched/core
Changes in v2: - rebased on top of v4.15-rc2 - tested that overhauled PELT code does not affect the util_est
.:: References ============== [1] https://lkml.org/lkml/2018/2/22/639 20180222170153.673-1-patrick.bellasi@arm.com [2] git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git sched/core (commit 083c6eeab2cc) [3] https://lkml.org/lkml/2018/1/23/645 20180123180847.4477-1-patrick.bellasi@arm.com
Patrick Bellasi (4): sched/fair: add util_est on top of PELT sched/fair: use util_est in LB and WU paths sched/cpufreq_schedutil: use util_est for OPP selection sched/fair: update util_est only on util_avg updates
include/linux/sched.h | 29 ++++++ kernel/sched/debug.c | 4 + kernel/sched/fair.c | 237 ++++++++++++++++++++++++++++++++++++++++++++---- kernel/sched/features.h | 5 + kernel/sched/sched.h | 9 +- 5 files changed, 264 insertions(+), 20 deletions(-)
-- 2.15.1
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