From: Vincent Guittot <vincent.guittot@linaro.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
Valentin Schneider <valentin.schneider@arm.com>,
Morten Rasmussen <morten.rasmussen@foss.arm.com>,
Brendan Jackman <brendan.jackman@arm.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>
Subject: Re: [PATCH v3 1/3] sched: Stop nohz stats when decayed
Date: Mon, 12 Feb 2018 10:52:11 +0100 [thread overview]
Message-ID: <CAKfTPtDGSOhK6Ly6So6EXjComTb==Rd1Bbt79syOtjsBnN5avQ@mail.gmail.com> (raw)
In-Reply-To: <20180212094115.GS25201@hirez.programming.kicks-ass.net>
On 12 February 2018 at 10:41, Peter Zijlstra <peterz@infradead.org> wrote:
> On Mon, Feb 12, 2018 at 09:07:52AM +0100, Vincent Guittot wrote:
>> @@ -9222,6 +9259,20 @@ void nohz_balance_enter_idle(int cpu)
>> atomic_inc(&nohz.nr_cpus);
>>
>> set_cpu_sd_state_idle(cpu);
>> +
>> + /*
>> + * Ensures that if nohz_idle_balance() fails to observe our
>> + * @idle_cpus_mask store, it must observe the @has_blocked
>> + * store.
>> + */
>> + smp_mb__after_atomic();
>> +
>> +out:
>> + /*
>> + * Each time a cpu enter idle, we assume that it has blocked load and
>> + * enable the periodic update of the load of idle cpus
>> + */
>> + WRITE_ONCE(nohz.has_blocked, 1);
>> }
>> #else
>> static inline void nohz_balancer_kick(struct rq *rq) { }
>
> I moved the barrier up one statement, such that its right after the
> atomic_inc(). Otherwise people will get all itchy about __after_atomic()
> semantics and we really only care about the cpumask_set_cpu() vs
> WRITE_ONCE() ordering, so it doesn't really matter _where_ that barrier
> lands in between.
ok. make sense
>
>> @@ -9374,6 +9425,22 @@ static bool nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle)
>>
>> SCHED_WARN_ON((flags & NOHZ_KICK_MASK) == NOHZ_BALANCE_KICK);
>>
>> + /*
>> + * We assume there will be no idle load after this update and clear
>> + * the has_blocked flag. If a cpu enters idle in the mean time, it will
>> + * set the has_blocked flag and trig another update of idle load.
>> + * Because a cpu that becomes idle, is added to idle_cpus_mask before
>> + * setting the flag, we are sure to not clear the state and not
>> + * check the load of an idle cpu.
>> + */
>> + WRITE_ONCE(nohz.has_blocked, 0);
>> +
>> + /*
>> + * Ensures that if we miss the CPU, we must see the has_blocked
>> + * store from nohz_balance_enter_idle().
>> + */
>> + smp_mb();
>> +
>> for_each_cpu(balance_cpu, nohz.idle_cpus_mask) {
>> if (balance_cpu == this_cpu || !idle_cpu(balance_cpu))
>> continue;
>
> Fixed that white space damage for you ;-)
Thanks
next prev parent reply other threads:[~2018-02-12 9:52 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-12 8:07 [PATCH v3 0/3] sched: Update blocked load Vincent Guittot
2018-02-12 8:07 ` [PATCH v3 1/3] sched: Stop nohz stats when decayed Vincent Guittot
2018-02-12 9:41 ` Peter Zijlstra
2018-02-12 9:52 ` Vincent Guittot [this message]
2018-02-12 10:45 ` Peter Zijlstra
2018-02-12 11:02 ` Vincent Guittot
2018-02-12 8:07 ` [PATCH v3 2/3] sched: reduce the periodic update duration Vincent Guittot
2018-02-12 8:07 ` [PATCH v3 3/3] sched: update blocked load when newly idle Vincent Guittot
2018-02-12 12:04 ` Peter Zijlstra
2018-02-12 14:34 ` Vincent Guittot
2018-02-12 15:38 ` Peter Zijlstra
2018-02-12 16:06 ` Vincent Guittot
2018-03-01 16:09 ` Frederic Weisbecker
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