[ NOTE: unfortunately this tree had to be freshly rebased today,
it's a same-content tree of 82891be90f3c (-next published)
merged with v5.11.
The main reason for the rebase was an authorship misattribution
problem with a new commit, which we noticed in the last minute,
and which we didn't want to be merged upstream. The offending
commit was deep in the tree, and dependent commits had to be
rebased as well. ]
- Core scheduler updates:
- Add CONFIG_PREEMPT_DYNAMIC: this in its current form adds the
preempt=none/voluntary/full boot options (default: full),
to allow distros to build a PREEMPT kernel but fall back to
close to PREEMPT_VOLUNTARY (or PREEMPT_NONE) runtime scheduling
behavior via a boot time selection.
There's also the /debug/sched_debug switch to do this runtime.
This feature is implemented via runtime patching (a new variant of static calls).
The scope of the runtime patching can be best reviewed by looking
at the sched_dynamic_update() function in kernel/sched/core.c.
( Note that the dynamic none/voluntary mode isn't 100% identical,
for example preempt-RCU is available in all cases, plus the
preempt count is maintained in all models, which has runtime
overhead even with the code patching. )
The PREEMPT_VOLUNTARY/PREEMPT_NONE models, used by the vast majority
of distributions, are supposed to be unaffected.
- Fix ignored rescheduling after rcu_eqs_enter(). This is a bug that
was found via rcutorture triggering a hang. The bug is that
rcu_idle_enter() may wake up a NOCB kthread, but this happens after
the last generic need_resched() check. Some cpuidle drivers fix it
by chance but many others don't.
In true 2020 fashion the original bug fix has grown into a 5-patch
scheduler/RCU fix series plus another 16 RCU patches to address
the underlying issue of missed preemption events. These are the
initial fixes that should fix current incarnations of the bug.
- Clean up rbtree usage in the scheduler, by providing & using the following
consistent set of rbtree APIs:
partial-order; less() based:
- rb_add(): add a new entry to the rbtree
- rb_add_cached(): like rb_add(), but for a rb_root_cached
total-order; cmp() based:
- rb_find(): find an entry in an rbtree
- rb_find_add(): find an entry, and add if not found
- rb_find_first(): find the first (leftmost) matching entry
- rb_next_match(): continue from rb_find_first()
- rb_for_each(): iterate a sub-tree using the previous two
- Improve the SMP/NUMA load-balancer: scan for an idle sibling in a single pass.
This is a 4-commit series where each commit improves one aspect of the idle
sibling scan logic.
- Improve the cpufreq cooling driver by getting the effective CPU utilization
metrics from the scheduler
- Improve the fair scheduler's active load-balancing logic by reducing the number
of active LB attempts & lengthen the load-balancing interval. This improves
stress-ng mmapfork performance.
- Fix CFS's estimated utilization (util_est) calculation bug that can result in
too high utilization values
- Misc updates & fixes:
- Fix the HRTICK reprogramming & optimization feature
- Fix SCHED_SOFTIRQ raising race & warning in the CPU offlining code
- Reduce dl_add_task_root_domain() overhead
- Fix uprobes refcount bug
- Process pending softirqs in flush_smp_call_function_from_idle()
- Clean up task priority related defines, remove *USER_*PRIO and
USER_PRIO()
- Simplify the sched_init_numa() deduplication sort
- Documentation updates
- Fix EAS bug in update_misfit_status(), which degraded the quality
of energy-balancing
- Smaller cleanups
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Merge tag 'sched-core-2021-02-17' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull scheduler updates from Ingo Molnar:
"Core scheduler updates:
- Add CONFIG_PREEMPT_DYNAMIC: this in its current form adds the
preempt=none/voluntary/full boot options (default: full), to allow
distros to build a PREEMPT kernel but fall back to close to
PREEMPT_VOLUNTARY (or PREEMPT_NONE) runtime scheduling behavior via
a boot time selection.
There's also the /debug/sched_debug switch to do this runtime.
This feature is implemented via runtime patching (a new variant of
static calls).
The scope of the runtime patching can be best reviewed by looking
at the sched_dynamic_update() function in kernel/sched/core.c.
( Note that the dynamic none/voluntary mode isn't 100% identical,
for example preempt-RCU is available in all cases, plus the
preempt count is maintained in all models, which has runtime
overhead even with the code patching. )
The PREEMPT_VOLUNTARY/PREEMPT_NONE models, used by the vast
majority of distributions, are supposed to be unaffected.
- Fix ignored rescheduling after rcu_eqs_enter(). This is a bug that
was found via rcutorture triggering a hang. The bug is that
rcu_idle_enter() may wake up a NOCB kthread, but this happens after
the last generic need_resched() check. Some cpuidle drivers fix it
by chance but many others don't.
In true 2020 fashion the original bug fix has grown into a 5-patch
scheduler/RCU fix series plus another 16 RCU patches to address the
underlying issue of missed preemption events. These are the initial
fixes that should fix current incarnations of the bug.
- Clean up rbtree usage in the scheduler, by providing & using the
following consistent set of rbtree APIs:
partial-order; less() based:
- rb_add(): add a new entry to the rbtree
- rb_add_cached(): like rb_add(), but for a rb_root_cached
total-order; cmp() based:
- rb_find(): find an entry in an rbtree
- rb_find_add(): find an entry, and add if not found
- rb_find_first(): find the first (leftmost) matching entry
- rb_next_match(): continue from rb_find_first()
- rb_for_each(): iterate a sub-tree using the previous two
- Improve the SMP/NUMA load-balancer: scan for an idle sibling in a
single pass. This is a 4-commit series where each commit improves
one aspect of the idle sibling scan logic.
- Improve the cpufreq cooling driver by getting the effective CPU
utilization metrics from the scheduler
- Improve the fair scheduler's active load-balancing logic by
reducing the number of active LB attempts & lengthen the
load-balancing interval. This improves stress-ng mmapfork
performance.
- Fix CFS's estimated utilization (util_est) calculation bug that can
result in too high utilization values
Misc updates & fixes:
- Fix the HRTICK reprogramming & optimization feature
- Fix SCHED_SOFTIRQ raising race & warning in the CPU offlining code
- Reduce dl_add_task_root_domain() overhead
- Fix uprobes refcount bug
- Process pending softirqs in flush_smp_call_function_from_idle()
- Clean up task priority related defines, remove *USER_*PRIO and
USER_PRIO()
- Simplify the sched_init_numa() deduplication sort
- Documentation updates
- Fix EAS bug in update_misfit_status(), which degraded the quality
of energy-balancing
- Smaller cleanups"
* tag 'sched-core-2021-02-17' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (51 commits)
sched,x86: Allow !PREEMPT_DYNAMIC
entry/kvm: Explicitly flush pending rcuog wakeup before last rescheduling point
entry: Explicitly flush pending rcuog wakeup before last rescheduling point
rcu/nocb: Trigger self-IPI on late deferred wake up before user resume
rcu/nocb: Perform deferred wake up before last idle's need_resched() check
rcu: Pull deferred rcuog wake up to rcu_eqs_enter() callers
sched/features: Distinguish between NORMAL and DEADLINE hrtick
sched/features: Fix hrtick reprogramming
sched/deadline: Reduce rq lock contention in dl_add_task_root_domain()
uprobes: (Re)add missing get_uprobe() in __find_uprobe()
smp: Process pending softirqs in flush_smp_call_function_from_idle()
sched: Harden PREEMPT_DYNAMIC
static_call: Allow module use without exposing static_call_key
sched: Add /debug/sched_preempt
preempt/dynamic: Support dynamic preempt with preempt= boot option
preempt/dynamic: Provide irqentry_exit_cond_resched() static call
preempt/dynamic: Provide preempt_schedule[_notrace]() static calls
preempt/dynamic: Provide cond_resched() and might_resched() static calls
preempt: Introduce CONFIG_PREEMPT_DYNAMIC
static_call: Provide DEFINE_STATIC_CALL_RET0()
...
657bd90c93