Messages in this thread | | | From | Pierre Gondois <> | Subject | [PATCH 0/7] sched/fair|isolation: Correctly clear nohz.[nr_cpus|idle_cpus_mask] for isolated CPUs | Date | Wed, 3 Apr 2024 17:05:32 +0200 |
| |
Zhang Rui reported that find_new_ilb() was iterating over CPUs in isolated cgroup partitions. This triggered spurious wakeups for theses CPUs. [1] The initial approach was to ignore CPUs on NULL sched domains, as isolated CPUs have a NULL sched domain. However a CPU: - with its tick disabled, so taken into account in nohz.[idle_cpus_mask|nr_cpus] - which is placed in an isolated cgroup partition will never update nohz.[idle_cpus_mask|nr_cpus] again.
To avoid that, the following variables should be cleared when a CPU is placed in an isolated cgroup partition: - nohz.idle_cpus_mask - nohz.nr_cpus - rq->nohz_tick_stopped This would allow to avoid considering wrong nohz.* values during idle load balance.
As suggested in [2] and to avoid calling nohz_balance_[enter|exit]_idle() from a remote CPU and create concurrency issues, leverage the existing housekeeping HK_TYPE_SCHED mask to reflect isolated CPUs (i.e. on NULL sched domains). Indeed the HK_TYPE_SCHED mask is currently never set by the isolcpus/nohz_full kernel parameters, so it defaults to cpu_online_mask. Plus it's current usage fits CPUs that are isolated and should not take part in load balancing.
Making use of HK_TYPE_SCHED for this purpose implies creating a housekeeping mask which can be modified at runtime.
[1] https://lore.kernel.org/all/20230804090858.7605-1-rui.zhang@intel.com/ [2] https://lore.kernel.org/all/CAKfTPtAMd_KNKhXXGk5MEibzzQUX3BFkWgxtEW2o8FFTX99DKw@mail.gmail.com/
Pierre Gondois (7): sched/isolation: Introduce housekeeping_runtime isolation sched/isolation: Move HK_TYPE_SCHED to housekeeping runtime sched/isolation: Use HKR_TYPE_SCHED in find_new_ilb() sched/fair: Move/add on_null_domain()/housekeeping_cpu() checks sched/topology: Remove CPUs with NULL sd from HKR_TYPE_SCHED mask sched/fair: Remove on_null_domain() and redundant checks sched/fair: Clear idle_cpus_mask for CPUs with NULL sd
include/linux/sched/isolation.h | 30 ++++++++++++++++++++- include/linux/sched/nohz.h | 2 ++ kernel/sched/fair.c | 44 +++++++++++++++++------------- kernel/sched/isolation.c | 48 ++++++++++++++++++++++++++++++++- kernel/sched/topology.c | 7 +++++ 5 files changed, 110 insertions(+), 21 deletions(-)
-- 2.25.1
| |