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Date:   Tue, 22 May 2018 16:26:24 +0530
From:   Viresh Kumar <viresh.kumar@linaro.org>
To:     Patrick Bellasi <patrick.bellasi@arm.com>
Cc:     "Joel Fernandes (Google.)" <joelaf@google.com>,
        linux-kernel@vger.kernel.org,
        "Joel Fernandes (Google)" <joel@joelfernandes.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Juri Lelli <juri.lelli@redhat.com>,
        Luca Abeni <luca.abeni@santannapisa.it>,
        Todd Kjos <tkjos@google.com>, claudio@evidence.eu.com,
        kernel-team@android.com, linux-pm@vger.kernel.org
Subject: Re: [PATCH v2] schedutil: Allow cpufreq requests to be made even
 when kthread kicked
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References: <20180518185501.173552-1-joel@joelfernandes.org>
 <20180522103415.cuutobi5kbhj4gcw@vireshk-i7>
 <20180522105157.GX30654@e110439-lin>
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On 22-05-18, 11:51, Patrick Bellasi wrote:
> It could happen, but using:
> 
>    raw_spin_lock_irqsave(&sg_policy->update_lock, flags);
>    freq = READ_ONCE(sg_policy->next_freq)
>    WRITE_ONCE(sg_policy->work_in_progress, false);
>    raw_spin_unlock_irqrestore(&sg_policy->update_lock, flags);
> 
>                        if (!READ_ONCE(sg_policy->work_in_progress)) {
>                            WRITE_ONCE(sg_policy->work_in_progress, true);
>                            irq_work_queue(&sg_policy->irq_work);
>                        }

I think its better to get locking in place for non-fast switching case in
single-policy systems right now.

> should fix it by enforcing the ordering as well as documenting the
> concurrent access.
> 
> However, in the "sched update" side, where do we have the sequence:
> 
>    sg_policy->next_freq = 0;
>    sg_policy->next_freq = real-next-freq;

Ah, that was just an example of what a compiler may do (though it shouldn't do).

-- 
viresh