Re: [PATCH 1/3] sched: Add new API wake_up_if_idle() to wake up the idle cpu

Daniel Lezcano
2014-08-21T03:48:15Z

On 08/21/2014 04:12 AM, Liu, Chuansheng wrote:
> Hello Daniel,
>
>> -----Original Message-----
>> From: Daniel Lezcano [mailto:daniel.lezcano@linaro.org]
>> Sent: Thursday, August 21, 2014 9:54 AM
>> To: Liu, Chuansheng; luto@amacapital.net; peterz@infradead.org;
>> rjw@rjwysocki.net; mingo@redhat.com
>> Cc: linux-pm@vger.kernel.org; linux-kernel@vger.kernel.org; Liu, Changcheng;
>> Wang, Xiaoming; Chakravarty, Souvik K
>> Subject: Re: [PATCH 1/3] sched: Add new API wake_up_if_idle() to wake up the
>> idle cpu
>>
>> On 08/18/2014 10:37 AM, Chuansheng Liu wrote:
>>> Implementing one new API wake_up_if_idle(), which is used to
>>> wake up the idle CPU.
>>
>> Is this patchset tested ? Did you check it solves the issue you were
>> facing ?
> We have done the basic test, and found the cores can exit C0 quickly with this patchset.
> Basically once the _TIF_NEED_RESCHED is set, then the poll_idle() can be broken.
>
> Please correct me if something is wrong, thanks.

Actually, it was not clear for me if this patch was a proposal or not.

I will review it.

Thanks

-- Daniel

>>> Suggested-by: Andy Lutomirski <luto@amacapital.net>
>>> Signed-off-by: Chuansheng Liu <chuansheng.liu@intel.com>
>>> ---
>>> include/linux/sched.h | 1 +
>>> kernel/sched/core.c | 16 ++++++++++++++++
>>> 2 files changed, 17 insertions(+)
>>>
>>> diff --git a/include/linux/sched.h b/include/linux/sched.h
>>> index 857ba40..3f89ac1 100644
>>> --- a/include/linux/sched.h
>>> +++ b/include/linux/sched.h
>>> @@ -1024,6 +1024,7 @@ struct sched_domain_topology_level {
>>> extern struct sched_domain_topology_level *sched_domain_topology;
>>>
>>> extern void set_sched_topology(struct sched_domain_topology_level *tl);
>>> +extern void wake_up_if_idle(int cpu);
>>>
>>> #ifdef CONFIG_SCHED_DEBUG
>>> # define SD_INIT_NAME(type) .name = #type
>>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>>> index 1211575..adf104f 100644
>>> --- a/kernel/sched/core.c
>>> +++ b/kernel/sched/core.c
>>> @@ -1620,6 +1620,22 @@ static void ttwu_queue_remote(struct
>> task_struct *p, int cpu)
>>> }
>>> }
>>>
>>> +void wake_up_if_idle(int cpu)
>>> +{
>>> + struct rq *rq = cpu_rq(cpu);
>>> + unsigned long flags;
>>> +
>>> + if (set_nr_if_polling(rq->idle)) {
>>> + trace_sched_wake_idle_without_ipi(cpu);
>>> + } else {
>>> + raw_spin_lock_irqsave(&rq->lock, flags);
>>> + if (rq->curr == rq->idle)
>>> + smp_send_reschedule(cpu);
>>> + /* Else cpu is not in idle, do nothing here */
>>> + raw_spin_unlock_irqrestore(&rq->lock, flags);
>>> + }
>>> +}
>>> +
>>> bool cpus_share_cache(int this_cpu, int that_cpu)
>>> {
>>> return per_cpu(sd_llc_id, this_cpu) == per_cpu(sd_llc_id, that_cpu);
>>>
>>
>>
>> --
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>> SoCs
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>

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