From: Subhra Mazumdar <subhra.mazumdar@oracle.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Viresh Kumar <viresh.kumar@linaro.org>,
Ingo Molnar <mingo@redhat.com>,
linux-kernel@vger.kernel.org,
Vincent Guittot <vincent.guittot@linaro.org>,
tkjos@google.com, Daniel Lezcano <daniel.lezcano@linaro.org>,
quentin.perret@linaro.org, chris.redpath@arm.com,
steven.sistare@oracle.com, songliubraving@fb.com
Subject: Re: [PATCH V3 2/2] sched/fair: Fallback to sched-idle CPU if idle CPU isn't found
Date: Tue, 2 Jul 2019 09:32:27 -0700 [thread overview]
Message-ID: <1fe415a7-a396-508c-f459-0ddcc36f3360@oracle.com> (raw)
In-Reply-To: <20190702083517.GY3419@hirez.programming.kicks-ass.net>
On 7/2/19 1:35 AM, Peter Zijlstra wrote:
> On Mon, Jul 01, 2019 at 03:08:41PM -0700, Subhra Mazumdar wrote:
>> On 7/1/19 1:03 AM, Viresh Kumar wrote:
>>> On 28-06-19, 18:16, Subhra Mazumdar wrote:
>>>> On 6/25/19 10:06 PM, Viresh Kumar wrote:
>>>>> @@ -5376,6 +5376,15 @@ static struct {
>>>>> #endif /* CONFIG_NO_HZ_COMMON */
>>>>> +/* CPU only has SCHED_IDLE tasks enqueued */
>>>>> +static int sched_idle_cpu(int cpu)
>>>>> +{
>>>>> + struct rq *rq = cpu_rq(cpu);
>>>>> +
>>>>> + return unlikely(rq->nr_running == rq->cfs.idle_h_nr_running &&
>>>>> + rq->nr_running);
>>>>> +}
>>>>> +
>>>> Shouldn't this check if rq->curr is also sched idle?
>>> Why wouldn't the current set of checks be enough to guarantee that ?
>> I thought nr_running does not include the on-cpu thread.
> It very much does.
>
>>>> And why not drop the rq->nr_running non zero check?
>>> Because CPU isn't sched-idle if nr_running and idle_h_nr_running are both 0,
>>> i.e. it is an IDLE cpu in that case. And so I thought it is important to have
>>> this check as well.
>>>
>> idle_cpu() not only checks nr_running is 0 but also rq->curr == rq->idle
> idle_cpu() will try very hard to declare a CPU !idle. But I don't see
> how that it relevant. sched_idle_cpu() will only return true if there
> are only SCHED_IDLE tasks on the CPU. Viresh's test is simple and
> straight forward.
OK makes sense.
Thanks,
Subhra
next prev parent reply other threads:[~2019-07-02 16:32 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-26 5:06 [PATCH V3 0/2] sched/fair: Fallback to sched-idle CPU in absence of idle CPUs Viresh Kumar
2019-06-26 5:06 ` [PATCH V3 1/2] sched: Start tracking SCHED_IDLE tasks count in cfs_rq Viresh Kumar
2019-07-25 16:15 ` [tip:sched/core] sched/fair: " tip-bot for Viresh Kumar
2019-06-26 5:06 ` [PATCH V3 2/2] sched/fair: Fallback to sched-idle CPU if idle CPU isn't found Viresh Kumar
2019-06-29 1:16 ` Subhra Mazumdar
2019-07-01 8:03 ` Viresh Kumar
2019-07-01 22:08 ` Subhra Mazumdar
2019-07-02 8:35 ` Peter Zijlstra
2019-07-02 16:32 ` Subhra Mazumdar [this message]
2019-07-25 16:16 ` [tip:sched/core] sched/fair: Fall back " tip-bot for Viresh Kumar
2019-07-01 13:43 ` [PATCH V3 0/2] sched/fair: Fallback to sched-idle CPU in absence of idle CPUs Peter Zijlstra
2019-07-03 9:13 ` Viresh Kumar
2019-12-09 3:50 ` Wanpeng Li
2019-12-10 6:33 ` Viresh Kumar
2019-12-10 11:15 ` Wanpeng Li
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