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| author | Will Deacon <will@kernel.org> | 2021-07-30 12:24:28 +0100 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2021-08-20 12:32:58 +0200 |
| commit | 9ae606bc74dd0e58d4de894e3c5cbb9d45599267 (patch) | |
| tree | d3459bdb6258212fb8e17196a3fb518c71afebca /include | |
| parent | 304000390f88d049c85e9a0958ac5567f38816ee (diff) | |
| download | lwn-9ae606bc74dd0e58d4de894e3c5cbb9d45599267.tar.gz lwn-9ae606bc74dd0e58d4de894e3c5cbb9d45599267.zip | |
sched: Introduce task_cpu_possible_mask() to limit fallback rq selection
Asymmetric systems may not offer the same level of userspace ISA support
across all CPUs, meaning that some applications cannot be executed by
some CPUs. As a concrete example, upcoming arm64 big.LITTLE designs do
not feature support for 32-bit applications on both clusters.
On such a system, we must take care not to migrate a task to an
unsupported CPU when forcefully moving tasks in select_fallback_rq()
in response to a CPU hot-unplug operation.
Introduce a task_cpu_possible_mask() hook which, given a task argument,
allows an architecture to return a cpumask of CPUs that are capable of
executing that task. The default implementation returns the
cpu_possible_mask, since sane machines do not suffer from per-cpu ISA
limitations that affect scheduling. The new mask is used when selecting
the fallback runqueue as a last resort before forcing a migration to the
first active CPU.
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Valentin Schneider <Valentin.Schneider@arm.com>
Reviewed-by: Quentin Perret <qperret@google.com>
Link: https://lore.kernel.org/r/20210730112443.23245-2-will@kernel.org
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/mmu_context.h | 14 |
1 files changed, 14 insertions, 0 deletions
diff --git a/include/linux/mmu_context.h b/include/linux/mmu_context.h index 03dee12d2b61..b9b970f7ab45 100644 --- a/include/linux/mmu_context.h +++ b/include/linux/mmu_context.h @@ -14,4 +14,18 @@ static inline void leave_mm(int cpu) { } #endif +/* + * CPUs that are capable of running user task @p. Must contain at least one + * active CPU. It is assumed that the kernel can run on all CPUs, so calling + * this for a kernel thread is pointless. + * + * By default, we assume a sane, homogeneous system. + */ +#ifndef task_cpu_possible_mask +# define task_cpu_possible_mask(p) cpu_possible_mask +# define task_cpu_possible(cpu, p) true +#else +# define task_cpu_possible(cpu, p) cpumask_test_cpu((cpu), task_cpu_possible_mask(p)) +#endif + #endif |