mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
synced 2025-01-22 07:53:11 -05:00
1d6d399223
1) Per-CPU kthreads must stay affine to a single CPU and never execute
relevant code on any other CPU. This is currently handled by smpboot
code which takes care of CPU-hotplug operations. Affinity here is
a correctness constraint.
2) Some kthreads _have_ to be affine to a specific set of CPUs and can't
run anywhere else. The affinity is set through kthread_bind_mask()
and the subsystem takes care by itself to handle CPU-hotplug
operations. Affinity here is assumed to be a correctness constraint.
3) Per-node kthreads _prefer_ to be affine to a specific NUMA node. This
is not a correctness constraint but merely a preference in terms of
memory locality. kswapd and kcompactd both fall into this category.
The affinity is set manually like for any other task and CPU-hotplug
is supposed to be handled by the relevant subsystem so that the task
is properly reaffined whenever a given CPU from the node comes up.
Also care should be taken so that the node affinity doesn't cross
isolated (nohz_full) cpumask boundaries.
4) Similar to the previous point except kthreads have a _preferred_
affinity different than a node. Both RCU boost kthreads and RCU
exp kworkers fall into this category as they refer to "RCU nodes"
from a distinctly distributed tree.
Currently the preferred affinity patterns (3 and 4) have at least 4
identified users, with more or less success when it comes to handle
CPU-hotplug operations and CPU isolation. Each of which do it in its own
ad-hoc way.
This is an infrastructure proposal to handle this with the following API
changes:
_ kthread_create_on_node() automatically affines the created kthread to
its target node unless it has been set as per-cpu or bound with
kthread_bind[_mask]() before the first wake-up.
- kthread_affine_preferred() is a new function that can be called right
after kthread_create_on_node() to specify a preferred affinity
different than the specified node.
When the preferred affinity can't be applied because the possible
targets are offline or isolated (nohz_full), the kthread is affine
to the housekeeping CPUs (which means to all online CPUs most of the
time or only the non-nohz_full CPUs when nohz_full= is set).
kswapd, kcompactd, RCU boost kthreads and RCU exp kworkers have been
converted, along with a few old drivers.
Summary of the changes:
* Consolidate a bunch of ad-hoc implementations of kthread_run_on_cpu()
* Introduce task_cpu_fallback_mask() that defines the default last
resort affinity of a task to become nohz_full aware
* Add some correctness check to ensure kthread_bind() is always called
before the first kthread wake up.
* Default affine kthread to its preferred node.
* Convert kswapd / kcompactd and remove their halfway working ad-hoc
affinity implementation
* Implement kthreads preferred affinity
* Unify kthread worker and kthread API's style
* Convert RCU kthreads to the new API and remove the ad-hoc affinity
implementation.
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Merge tag 'kthread-for-6.14-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks
Pull kthread updates from Frederic Weisbecker:
"Kthreads affinity follow either of 4 existing different patterns:
1) Per-CPU kthreads must stay affine to a single CPU and never
execute relevant code on any other CPU. This is currently handled
by smpboot code which takes care of CPU-hotplug operations.
Affinity here is a correctness constraint.
2) Some kthreads _have_ to be affine to a specific set of CPUs and
can't run anywhere else. The affinity is set through
kthread_bind_mask() and the subsystem takes care by itself to
handle CPU-hotplug operations. Affinity here is assumed to be a
correctness constraint.
3) Per-node kthreads _prefer_ to be affine to a specific NUMA node.
This is not a correctness constraint but merely a preference in
terms of memory locality. kswapd and kcompactd both fall into this
category. The affinity is set manually like for any other task and
CPU-hotplug is supposed to be handled by the relevant subsystem so
that the task is properly reaffined whenever a given CPU from the
node comes up. Also care should be taken so that the node affinity
doesn't cross isolated (nohz_full) cpumask boundaries.
4) Similar to the previous point except kthreads have a _preferred_
affinity different than a node. Both RCU boost kthreads and RCU
exp kworkers fall into this category as they refer to "RCU nodes"
from a distinctly distributed tree.
Currently the preferred affinity patterns (3 and 4) have at least 4
identified users, with more or less success when it comes to handle
CPU-hotplug operations and CPU isolation. Each of which do it in its
own ad-hoc way.
This is an infrastructure proposal to handle this with the following
API changes:
- kthread_create_on_node() automatically affines the created kthread
to its target node unless it has been set as per-cpu or bound with
kthread_bind[_mask]() before the first wake-up.
- kthread_affine_preferred() is a new function that can be called
right after kthread_create_on_node() to specify a preferred
affinity different than the specified node.
When the preferred affinity can't be applied because the possible
targets are offline or isolated (nohz_full), the kthread is affine to
the housekeeping CPUs (which means to all online CPUs most of the time
or only the non-nohz_full CPUs when nohz_full= is set).
kswapd, kcompactd, RCU boost kthreads and RCU exp kworkers have been
converted, along with a few old drivers.
Summary of the changes:
- Consolidate a bunch of ad-hoc implementations of
kthread_run_on_cpu()
- Introduce task_cpu_fallback_mask() that defines the default last
resort affinity of a task to become nohz_full aware
- Add some correctness check to ensure kthread_bind() is always
called before the first kthread wake up.
- Default affine kthread to its preferred node.
- Convert kswapd / kcompactd and remove their halfway working ad-hoc
affinity implementation
- Implement kthreads preferred affinity
- Unify kthread worker and kthread API's style
- Convert RCU kthreads to the new API and remove the ad-hoc affinity
implementation"
* tag 'kthread-for-6.14-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks:
kthread: modify kernel-doc function name to match code
rcu: Use kthread preferred affinity for RCU exp kworkers
treewide: Introduce kthread_run_worker[_on_cpu]()
kthread: Unify kthread_create_on_cpu() and kthread_create_worker_on_cpu() automatic format
rcu: Use kthread preferred affinity for RCU boost
kthread: Implement preferred affinity
mm: Create/affine kswapd to its preferred node
mm: Create/affine kcompactd to its preferred node
kthread: Default affine kthread to its preferred NUMA node
kthread: Make sure kthread hasn't started while binding it
sched,arm64: Handle CPU isolation on last resort fallback rq selection
arm64: Exclude nohz_full CPUs from 32bits el0 support
lib: test_objpool: Use kthread_run_on_cpu()
kallsyms: Use kthread_run_on_cpu()
soc/qman: test: Use kthread_run_on_cpu()
arm/bL_switcher: Use kthread_run_on_cpu()
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|---|---|---|
| .. | ||
| acpi-cpufreq.c | ||
| amd-pstate-trace.c | ||
| amd-pstate-trace.h | ||
| amd-pstate-ut.c | ||
| amd-pstate.c | ||
| amd-pstate.h | ||
| amd_freq_sensitivity.c | ||
| apple-soc-cpufreq.c | ||
| armada-8k-cpufreq.c | ||
| armada-37xx-cpufreq.c | ||
| bmips-cpufreq.c | ||
| brcmstb-avs-cpufreq.c | ||
| cppc_cpufreq.c | ||
| cpufreq-dt-platdev.c | ||
| cpufreq-dt.c | ||
| cpufreq-dt.h | ||
| cpufreq-nforce2.c | ||
| cpufreq.c | ||
| cpufreq_conservative.c | ||
| cpufreq_governor.c | ||
| cpufreq_governor.h | ||
| cpufreq_governor_attr_set.c | ||
| cpufreq_ondemand.c | ||
| cpufreq_ondemand.h | ||
| cpufreq_performance.c | ||
| cpufreq_powersave.c | ||
| cpufreq_stats.c | ||
| cpufreq_userspace.c | ||
| davinci-cpufreq.c | ||
| e_powersaver.c | ||
| elanfreq.c | ||
| freq_table.c | ||
| gx-suspmod.c | ||
| highbank-cpufreq.c | ||
| imx-cpufreq-dt.c | ||
| imx6q-cpufreq.c | ||
| intel_pstate.c | ||
| Kconfig | ||
| Kconfig.arm | ||
| Kconfig.powerpc | ||
| Kconfig.x86 | ||
| kirkwood-cpufreq.c | ||
| longhaul.c | ||
| longhaul.h | ||
| longrun.c | ||
| loongson2_cpufreq.c | ||
| loongson3_cpufreq.c | ||
| Makefile | ||
| mediatek-cpufreq-hw.c | ||
| mediatek-cpufreq.c | ||
| mvebu-cpufreq.c | ||
| omap-cpufreq.c | ||
| p4-clockmod.c | ||
| pasemi-cpufreq.c | ||
| pcc-cpufreq.c | ||
| pmac32-cpufreq.c | ||
| pmac64-cpufreq.c | ||
| powernow-k6.c | ||
| powernow-k7.c | ||
| powernow-k7.h | ||
| powernow-k8.c | ||
| powernow-k8.h | ||
| powernv-cpufreq.c | ||
| ppc_cbe_cpufreq.c | ||
| ppc_cbe_cpufreq.h | ||
| ppc_cbe_cpufreq_pervasive.c | ||
| ppc_cbe_cpufreq_pmi.c | ||
| pxa2xx-cpufreq.c | ||
| pxa3xx-cpufreq.c | ||
| qcom-cpufreq-hw.c | ||
| qcom-cpufreq-nvmem.c | ||
| qoriq-cpufreq.c | ||
| raspberrypi-cpufreq.c | ||
| s3c64xx-cpufreq.c | ||
| s5pv210-cpufreq.c | ||
| sa1110-cpufreq.c | ||
| sc520_freq.c | ||
| scmi-cpufreq.c | ||
| scpi-cpufreq.c | ||
| sh-cpufreq.c | ||
| sparc-us2e-cpufreq.c | ||
| sparc-us3-cpufreq.c | ||
| spear-cpufreq.c | ||
| speedstep-centrino.c | ||
| speedstep-ich.c | ||
| speedstep-lib.c | ||
| speedstep-lib.h | ||
| speedstep-smi.c | ||
| sti-cpufreq.c | ||
| sun50i-cpufreq-nvmem.c | ||
| tegra20-cpufreq.c | ||
| tegra124-cpufreq.c | ||
| tegra186-cpufreq.c | ||
| tegra194-cpufreq.c | ||
| ti-cpufreq.c | ||
| vexpress-spc-cpufreq.c | ||
| virtual-cpufreq.c | ||