| Message ID | 20210518094725.7701-9-will@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Add support for 32-bit tasks on asymmetric AArch32 systems | expand |
On 05/18/21 10:47, Will Deacon wrote: > 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. > > Modify guarantee_online_cpus() to take task_cpu_possible_mask() into > account when trying to find a suitable set of online CPUs for a given > task. This will avoid passing an invalid mask to set_cpus_allowed_ptr() > during ->attach() and will subsequently allow the cpuset hierarchy to be > taken into account when forcefully overriding the affinity mask for a > task which requires migration to a compatible CPU. > > Cc: Li Zefan <lizefan@huawei.com> > Cc: Tejun Heo <tj@kernel.org> > Cc: Johannes Weiner <hannes@cmpxchg.org> > Signed-off-by: Will Deacon <will@kernel.org> > --- > include/linux/cpuset.h | 2 +- > kernel/cgroup/cpuset.c | 33 +++++++++++++++++++-------------- > 2 files changed, 20 insertions(+), 15 deletions(-) > > diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h > index ed6ec677dd6b..414a8e694413 100644 > --- a/include/linux/cpuset.h > +++ b/include/linux/cpuset.h > @@ -185,7 +185,7 @@ static inline void cpuset_read_unlock(void) { } > static inline void cpuset_cpus_allowed(struct task_struct *p, > struct cpumask *mask) > { > - cpumask_copy(mask, cpu_possible_mask); > + cpumask_copy(mask, task_cpu_possible_mask(p)); > } > > static inline void cpuset_cpus_allowed_fallback(struct task_struct *p) > diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c > index 8c799260a4a2..b532a5333ff9 100644 > --- a/kernel/cgroup/cpuset.c > +++ b/kernel/cgroup/cpuset.c > @@ -372,18 +372,26 @@ static inline bool is_in_v2_mode(void) > } > > /* > - * Return in pmask the portion of a cpusets's cpus_allowed that > - * are online. If none are online, walk up the cpuset hierarchy > - * until we find one that does have some online cpus. > + * Return in pmask the portion of a task's cpusets's cpus_allowed that > + * are online and are capable of running the task. If none are found, > + * walk up the cpuset hierarchy until we find one that does have some > + * appropriate cpus. > * > * One way or another, we guarantee to return some non-empty subset > * of cpu_online_mask. > * > * Call with callback_lock or cpuset_mutex held. > */ > -static void guarantee_online_cpus(struct cpuset *cs, struct cpumask *pmask) > +static void guarantee_online_cpus(struct task_struct *tsk, > + struct cpumask *pmask) > { > - while (!cpumask_intersects(cs->effective_cpus, cpu_online_mask)) { > + struct cpuset *cs = task_cs(tsk); task_cs() requires rcu_read_lock(), but I can't see how the lock is obtained from cpuset_attach() path, did I miss it? Running with lockdep should spill suspicious RCU usage warning. Maybe it makes more sense to move the rcu_read_lock() inside the function now with task_cs()? Thanks -- Qais Yousef > + const struct cpumask *possible_mask = task_cpu_possible_mask(tsk); > + > + if (WARN_ON(!cpumask_and(pmask, possible_mask, cpu_online_mask))) > + cpumask_copy(pmask, cpu_online_mask); > + > + while (!cpumask_intersects(cs->effective_cpus, pmask)) { > cs = parent_cs(cs); > if (unlikely(!cs)) { > /* > @@ -393,11 +401,10 @@ static void guarantee_online_cpus(struct cpuset *cs, struct cpumask *pmask) > * cpuset's effective_cpus is on its way to be > * identical to cpu_online_mask. > */ > - cpumask_copy(pmask, cpu_online_mask); > return; > } > } > - cpumask_and(pmask, cs->effective_cpus, cpu_online_mask); > + cpumask_and(pmask, pmask, cs->effective_cpus); > } > > /* > @@ -2199,15 +2206,13 @@ static void cpuset_attach(struct cgroup_taskset *tset) > > percpu_down_write(&cpuset_rwsem); > > - /* prepare for attach */ > - if (cs == &top_cpuset) > - cpumask_copy(cpus_attach, cpu_possible_mask); > - else > - guarantee_online_cpus(cs, cpus_attach); > - > guarantee_online_mems(cs, &cpuset_attach_nodemask_to); > > cgroup_taskset_for_each(task, css, tset) { > + if (cs != &top_cpuset) > + guarantee_online_cpus(task, cpus_attach); > + else > + cpumask_copy(cpus_attach, task_cpu_possible_mask(task)); > /* > * can_attach beforehand should guarantee that this doesn't > * fail. TODO: have a better way to handle failure here > @@ -3303,7 +3308,7 @@ void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask) > > spin_lock_irqsave(&callback_lock, flags); > rcu_read_lock(); > - guarantee_online_cpus(task_cs(tsk), pmask); > + guarantee_online_cpus(tsk, pmask); > rcu_read_unlock(); > spin_unlock_irqrestore(&callback_lock, flags); > } > -- > 2.31.1.751.gd2f1c929bd-goog >
On Fri, May 21, 2021 at 05:25:24PM +0100, Qais Yousef wrote: > On 05/18/21 10:47, Will Deacon wrote: > > 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. > > > > Modify guarantee_online_cpus() to take task_cpu_possible_mask() into > > account when trying to find a suitable set of online CPUs for a given > > task. This will avoid passing an invalid mask to set_cpus_allowed_ptr() > > during ->attach() and will subsequently allow the cpuset hierarchy to be > > taken into account when forcefully overriding the affinity mask for a > > task which requires migration to a compatible CPU. > > > > Cc: Li Zefan <lizefan@huawei.com> > > Cc: Tejun Heo <tj@kernel.org> > > Cc: Johannes Weiner <hannes@cmpxchg.org> > > Signed-off-by: Will Deacon <will@kernel.org> > > --- > > include/linux/cpuset.h | 2 +- > > kernel/cgroup/cpuset.c | 33 +++++++++++++++++++-------------- > > 2 files changed, 20 insertions(+), 15 deletions(-) > > > > diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h > > index ed6ec677dd6b..414a8e694413 100644 > > --- a/include/linux/cpuset.h > > +++ b/include/linux/cpuset.h > > @@ -185,7 +185,7 @@ static inline void cpuset_read_unlock(void) { } > > static inline void cpuset_cpus_allowed(struct task_struct *p, > > struct cpumask *mask) > > { > > - cpumask_copy(mask, cpu_possible_mask); > > + cpumask_copy(mask, task_cpu_possible_mask(p)); > > } > > > > static inline void cpuset_cpus_allowed_fallback(struct task_struct *p) > > diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c > > index 8c799260a4a2..b532a5333ff9 100644 > > --- a/kernel/cgroup/cpuset.c > > +++ b/kernel/cgroup/cpuset.c > > @@ -372,18 +372,26 @@ static inline bool is_in_v2_mode(void) > > } > > > > /* > > - * Return in pmask the portion of a cpusets's cpus_allowed that > > - * are online. If none are online, walk up the cpuset hierarchy > > - * until we find one that does have some online cpus. > > + * Return in pmask the portion of a task's cpusets's cpus_allowed that > > + * are online and are capable of running the task. If none are found, > > + * walk up the cpuset hierarchy until we find one that does have some > > + * appropriate cpus. > > * > > * One way or another, we guarantee to return some non-empty subset > > * of cpu_online_mask. > > * > > * Call with callback_lock or cpuset_mutex held. > > */ > > -static void guarantee_online_cpus(struct cpuset *cs, struct cpumask *pmask) > > +static void guarantee_online_cpus(struct task_struct *tsk, > > + struct cpumask *pmask) > > { > > - while (!cpumask_intersects(cs->effective_cpus, cpu_online_mask)) { > > + struct cpuset *cs = task_cs(tsk); > > task_cs() requires rcu_read_lock(), but I can't see how the lock is obtained > from cpuset_attach() path, did I miss it? Running with lockdep should spill > suspicious RCU usage warning. > > Maybe it makes more sense to move the rcu_read_lock() inside the function now > with task_cs()? Well spotted! I'll add the rcu_read_[un]lock() calls to guarantee_online_cpus(). Will
diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h index ed6ec677dd6b..414a8e694413 100644 --- a/include/linux/cpuset.h +++ b/include/linux/cpuset.h @@ -185,7 +185,7 @@ static inline void cpuset_read_unlock(void) { } static inline void cpuset_cpus_allowed(struct task_struct *p, struct cpumask *mask) { - cpumask_copy(mask, cpu_possible_mask); + cpumask_copy(mask, task_cpu_possible_mask(p)); } static inline void cpuset_cpus_allowed_fallback(struct task_struct *p) diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index 8c799260a4a2..b532a5333ff9 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -372,18 +372,26 @@ static inline bool is_in_v2_mode(void) } /* - * Return in pmask the portion of a cpusets's cpus_allowed that - * are online. If none are online, walk up the cpuset hierarchy - * until we find one that does have some online cpus. + * Return in pmask the portion of a task's cpusets's cpus_allowed that + * are online and are capable of running the task. If none are found, + * walk up the cpuset hierarchy until we find one that does have some + * appropriate cpus. * * One way or another, we guarantee to return some non-empty subset * of cpu_online_mask. * * Call with callback_lock or cpuset_mutex held. */ -static void guarantee_online_cpus(struct cpuset *cs, struct cpumask *pmask) +static void guarantee_online_cpus(struct task_struct *tsk, + struct cpumask *pmask) { - while (!cpumask_intersects(cs->effective_cpus, cpu_online_mask)) { + struct cpuset *cs = task_cs(tsk); + const struct cpumask *possible_mask = task_cpu_possible_mask(tsk); + + if (WARN_ON(!cpumask_and(pmask, possible_mask, cpu_online_mask))) + cpumask_copy(pmask, cpu_online_mask); + + while (!cpumask_intersects(cs->effective_cpus, pmask)) { cs = parent_cs(cs); if (unlikely(!cs)) { /* @@ -393,11 +401,10 @@ static void guarantee_online_cpus(struct cpuset *cs, struct cpumask *pmask) * cpuset's effective_cpus is on its way to be * identical to cpu_online_mask. */ - cpumask_copy(pmask, cpu_online_mask); return; } } - cpumask_and(pmask, cs->effective_cpus, cpu_online_mask); + cpumask_and(pmask, pmask, cs->effective_cpus); } /* @@ -2199,15 +2206,13 @@ static void cpuset_attach(struct cgroup_taskset *tset) percpu_down_write(&cpuset_rwsem); - /* prepare for attach */ - if (cs == &top_cpuset) - cpumask_copy(cpus_attach, cpu_possible_mask); - else - guarantee_online_cpus(cs, cpus_attach); - guarantee_online_mems(cs, &cpuset_attach_nodemask_to); cgroup_taskset_for_each(task, css, tset) { + if (cs != &top_cpuset) + guarantee_online_cpus(task, cpus_attach); + else + cpumask_copy(cpus_attach, task_cpu_possible_mask(task)); /* * can_attach beforehand should guarantee that this doesn't * fail. TODO: have a better way to handle failure here @@ -3303,7 +3308,7 @@ void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask) spin_lock_irqsave(&callback_lock, flags); rcu_read_lock(); - guarantee_online_cpus(task_cs(tsk), pmask); + guarantee_online_cpus(tsk, pmask); rcu_read_unlock(); spin_unlock_irqrestore(&callback_lock, flags); }
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. Modify guarantee_online_cpus() to take task_cpu_possible_mask() into account when trying to find a suitable set of online CPUs for a given task. This will avoid passing an invalid mask to set_cpus_allowed_ptr() during ->attach() and will subsequently allow the cpuset hierarchy to be taken into account when forcefully overriding the affinity mask for a task which requires migration to a compatible CPU. Cc: Li Zefan <lizefan@huawei.com> Cc: Tejun Heo <tj@kernel.org> Cc: Johannes Weiner <hannes@cmpxchg.org> Signed-off-by: Will Deacon <will@kernel.org> --- include/linux/cpuset.h | 2 +- kernel/cgroup/cpuset.c | 33 +++++++++++++++++++-------------- 2 files changed, 20 insertions(+), 15 deletions(-)