Kernel/linux-stable
1
0
Fork 0
mirror of https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git synced 2025-01-04 04:06:26 +00:00
Code Issues Actions Packages Projects Releases Wiki Activity

sched: Introduce task_cpu_possible_mask() to limit fallback rq selection

Browse Source 
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
This commit is contained in:
Will Deacon 2021-07-30 12:24:28 +01:00 committed by Peter Zijlstra
parent 304000390f
commit 9ae606bc74
2 changed files with 17 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
include/linux/mmu_context.h
View File

@ -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

9
kernel/sched/core.c
View File

@ -2173,7 +2173,7 @@ static inline bool is_cpu_allowed(struct task_struct *p, int cpu)
/* Non kernel threads are not allowed during either online or offline. */
if (!(p->flags & PF_KTHREAD))
return cpu_active(cpu);
return cpu_active(cpu) && task_cpu_possible(cpu, p);
/* KTHREAD_IS_PER_CPU is always allowed. */
if (kthread_is_per_cpu(p))
@ -3124,9 +3124,7 @@ static int select_fallback_rq(int cpu, struct task_struct *p)
/* Look for allowed, online CPU in same node. */
for_each_cpu(dest_cpu, nodemask) {
if (!cpu_active(dest_cpu))
continue;
if (cpumask_test_cpu(dest_cpu, p->cpus_ptr))
if (is_cpu_allowed(p, dest_cpu))
return dest_cpu;
}
}
@ -3156,10 +3154,9 @@ static int select_fallback_rq(int cpu, struct task_struct *p)
*
* More yuck to audit.
*/
do_set_cpus_allowed(p, cpu_possible_mask);
do_set_cpus_allowed(p, task_cpu_possible_mask(p));
state = fail;
break;
case fail:
BUG();
break;