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Date: Sat, 1 Feb 2020 08:33:34 +0530 From: Prateek Sood <prsood@...eaurora.org> To: tj@...nel.org, peterz@...radead.org Cc: cgroups@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH] cpuset: Make cpuset hotplug synchronous Hi Tejun & Peter, Could you please share your feedback on this patch for making cpuset_hotplug_workfn synchronous. Thanks, Prateek On 1/24/2020 8:37 PM, Prateek Sood wrote: > Hi Tejun & Peter, > > It seems that after following patch we can make cpuset_hotplug_workfn > synchronous: > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/kernel/cgroup/cpuset.c?h=v5.5-rc7&id=d74b27d63a8bebe2fe634944e4ebdc7b10db7a39 > > > Could you please share your opinion on the same and below patch. > > Thanks, > Prateek > >> 8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8>8 > Convert cpuset_hotplug_workfn() into synchronous call for cpu hotplug > path. For memory hotplug path it still gets queued as a work item. > > Since cpuset_hotplug_workfn() can be made synchronous for cpu hotplug > path, it is not required to wait for cpuset hotplug while thawing > processes. > > Signed-off-by: Prateek Sood <prsood@...eaurora.org> > --- > include/linux/cpuset.h | 3 --- > kernel/cgroup/cpuset.c | 31 +++++++++++++++++++------------ > kernel/power/process.c | 2 -- > 3 files changed, 19 insertions(+), 17 deletions(-) > > diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h > index 04c20de66..cede4cb 100644 > --- a/include/linux/cpuset.h > +++ b/include/linux/cpuset.h > @@ -54,7 +54,6 @@ static inline void cpuset_dec(void) > extern void cpuset_init_smp(void); > extern void cpuset_force_rebuild(void); > extern void cpuset_update_active_cpus(void); > -extern void cpuset_wait_for_hotplug(void); > extern void cpuset_read_lock(void); > extern void cpuset_read_unlock(void); > extern void cpuset_cpus_allowed(struct task_struct *p, struct cpumask *mask); > @@ -176,8 +175,6 @@ static inline void cpuset_update_active_cpus(void) > partition_sched_domains(1, NULL, NULL); > } > > -static inline void cpuset_wait_for_hotplug(void) { } > - > static inline void cpuset_read_lock(void) { } > static inline void cpuset_read_unlock(void) { } > > diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c > index 58f5073..cafd4d2 100644 > --- a/kernel/cgroup/cpuset.c > +++ b/kernel/cgroup/cpuset.c > @@ -3101,7 +3101,7 @@ static void cpuset_hotplug_update_tasks(struct cpuset *cs, struct tmpmasks *tmp) > } > > /** > - * cpuset_hotplug_workfn - handle CPU/memory hotunplug for a cpuset > + * cpuset_hotplug - handle CPU/memory hotunplug for a cpuset > * > * This function is called after either CPU or memory configuration has > * changed and updates cpuset accordingly. The top_cpuset is always > @@ -3116,7 +3116,7 @@ static void cpuset_hotplug_update_tasks(struct cpuset *cs, struct tmpmasks *tmp) > * Note that CPU offlining during suspend is ignored. We don't modify > * cpusets across suspend/resume cycles at all. > */ > -static void cpuset_hotplug_workfn(struct work_struct *work) > +static void cpuset_hotplug(bool use_cpu_hp_lock) > { > static cpumask_t new_cpus; > static nodemask_t new_mems; > @@ -3201,25 +3201,32 @@ static void cpuset_hotplug_workfn(struct work_struct *work) > /* rebuild sched domains if cpus_allowed has changed */ > if (cpus_updated || force_rebuild) { > force_rebuild = false; > - rebuild_sched_domains(); > + if (use_cpu_hp_lock) > + rebuild_sched_domains(); > + else { > + /* Acquiring cpu_hotplug_lock is not required. > + * When cpuset_hotplug() is called in hotplug path, > + * cpu_hotplug_lock is held by the hotplug context > + * which is waiting for cpuhp_thread_fun to indicate > + * completion of callback. > + */ > + percpu_down_write(&cpuset_rwsem); > + rebuild_sched_domains_locked(); > + percpu_up_write(&cpuset_rwsem); > + } > } > > free_cpumasks(NULL, ptmp); > } > > -void cpuset_update_active_cpus(void) > +static void cpuset_hotplug_workfn(struct work_struct *work) > { > - /* > - * We're inside cpu hotplug critical region which usually nests > - * inside cgroup synchronization. Bounce actual hotplug processing > - * to a work item to avoid reverse locking order. > - */ > - schedule_work(&cpuset_hotplug_work); > + cpuset_hotplug(true); > } > > -void cpuset_wait_for_hotplug(void) > +void cpuset_update_active_cpus(void) > { > - flush_work(&cpuset_hotplug_work); > + cpuset_hotplug(false); > } > > /* > diff --git a/kernel/power/process.c b/kernel/power/process.c > index 4b6a54d..08f7019 100644 > --- a/kernel/power/process.c > +++ b/kernel/power/process.c > @@ -204,8 +204,6 @@ void thaw_processes(void) > __usermodehelper_set_disable_depth(UMH_FREEZING); > thaw_workqueues(); > > - cpuset_wait_for_hotplug(); > - > read_lock(&tasklist_lock); > for_each_process_thread(g, p) { > /* No other threads should have PF_SUSPEND_TASK set */ -- Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc., is a member of Code Aurora Forum, a Linux Foundation Collaborative Project
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