[RFC 01/11] sched: introduce sys_cpumask in tsk to adapt asymmetric system

[Liu ping fan]

On Wed, Nov 12, 2014 at 5:22 PM, Srikar Dronamraju
<srikar at linux.vnet.ibm.com> wrote:
> * kernelfans at gmail.com <kernelfans at gmail.com> [2014-10-16 15:29:50]:
>
>> Some system such as powerpc, some tsk (vcpu thread) can only run on
>> the dedicated cpu. Since we adapt some asymmetric method to monitor the
>> whole physical cpu. (powerKVM only allows the primary hwthread to
>> set up runtime env for the secondary when entering guest).
>>
>> Nowadays, powerKVM run with all the secondary hwthread offline to ensure
>> the vcpu threads only run on the primary thread. But we plan to keep all
>> cpus online when running powerKVM to give more power when switching back
>> to host, so introduce sys_allowed cpumask to reflect the cpuset which
>> the vcpu thread can run on.
>>
>> Signed-off-by: Liu Ping Fan <pingfank at linux.vnet.ibm.com>
>> ---
>>  include/linux/init_task.h |  1 +
>>  include/linux/sched.h     |  6 ++++++
>>  kernel/sched/core.c       | 10 ++++++++--
>>  3 files changed, 15 insertions(+), 2 deletions(-)
>>
>> diff --git a/include/linux/init_task.h b/include/linux/init_task.h
>> index 2bb4c4f3..c56f69e 100644
>> --- a/include/linux/init_task.h
>> +++ b/include/linux/init_task.h
>> @@ -172,6 +172,7 @@ extern struct task_group root_task_group;
>>       .normal_prio    = MAX_PRIO-20,                                  \
>>       .policy         = SCHED_NORMAL,                                 \
>>       .cpus_allowed   = CPU_MASK_ALL,                                 \
>> +     .sys_allowed = CPU_MASK_ALL,                    \
>
> Do we really need another mask, cant we just use cpus_allowed itself.
>
I think it is not easy to cast two request: chip inherit and user's
configuration onto one mask.

>>       .nr_cpus_allowed= NR_CPUS,                                      \
>>       .mm             = NULL,                                         \
>>       .active_mm      = &init_mm,                                     \
>> diff --git a/include/linux/sched.h b/include/linux/sched.h
>> index 5c2c885..ce429f3 100644
>> --- a/include/linux/sched.h
>> +++ b/include/linux/sched.h
>> @@ -1260,7 +1260,10 @@ struct task_struct {
>>
>>       unsigned int policy;
>>       int nr_cpus_allowed;
>> +     /* Anded user and sys_allowed */
>>       cpumask_t cpus_allowed;
>> +     /* due to the feature of asymmetric, some tsk can only run on such cpu */
>> +     cpumask_t sys_allowed;
>>
>>  #ifdef CONFIG_PREEMPT_RCU
>>       int rcu_read_lock_nesting;
>> @@ -2030,6 +2033,9 @@ static inline void tsk_restore_flags(struct task_struct *task,
>>  }
>>
>>  #ifdef CONFIG_SMP
>> +extern void set_cpus_sys_allowed(struct task_struct *p,
>> +                     const struct cpumask *new_mask);
>> +
>>  extern void do_set_cpus_allowed(struct task_struct *p,
>>                              const struct cpumask *new_mask);
>>
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index ec1a286..2cd1ae3 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -4596,13 +4596,19 @@ void init_idle(struct task_struct *idle, int cpu)
>>  }
>>
>>  #ifdef CONFIG_SMP
>> +void set_cpus_sys_allowed(struct task_struct *p,
>> +     const struct cpumask *new_mask)
>> +{
>> +     cpumask_copy(&p->sys_allowed, new_mask);
>> +}
>> +
>
> This function doesnt seem to be used anywhere... Not sure why it is
> introduced
>
Not layered the patches well :(  It is used later in the series.

Thx,
Fan

>>  void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)
>>  {
>>       if (p->sched_class && p->sched_class->set_cpus_allowed)
>>               p->sched_class->set_cpus_allowed(p, new_mask);
>>
>> -     cpumask_copy(&p->cpus_allowed, new_mask);
>> -     p->nr_cpus_allowed = cpumask_weight(new_mask);
>> +     cpumask_and(&p->cpus_allowed, &p->sys_allowed, new_mask);
>> +     p->nr_cpus_allowed = cpumask_weight(&p->cpus_allowed);
>>  }
>>
>>  /*
>> --
>> 1.8.3.1
>>
>>
>
> --
> Thanks and Regards
> Srikar Dronamraju
>