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Date: Thu, 21 Apr 2016 14:33:41 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Wanpeng Li <kernellwp@gmail.com>
Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Ingo Molnar <mingo@redhat.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Wanpeng Li <wanpeng.li@hotmail.com>,
        Linux PM list <linux-pm@vger.kernel.org>,
        Steve Muckle <steve.muckle@linaro.org>
Subject: Re: [PATCH] sched/cpufreq: don't trigger cpufreq update w/o real
 rt/deadline tasks running
Message-ID: <20160421123341.GJ3408@twins.programming.kicks-ass.net>
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On Thu, Apr 21, 2016 at 09:09:43AM +0800, Wanpeng Li wrote:
> >> Sometimes .update_curr hook is called w/o tasks actually running, it is
> >> captured by:
> >>
> >>          u64 delta_exec = rq_clock_task(rq) - curr->se.exec_start;
> >>
> >> We should not trigger cpufreq update in this case for rt/deadline
> >> classes, and this patch fix it.

> I add a print to print when delta_exec is zero for rt class, something

So its zero, so what?

> like below:

>       watchdog/5-48    [005] d...   568.449105: update_curr_rt: rt
> delta_exec is zero
>       watchdog/5-48    [005] d...   568.449111: <stack trace>
>  => put_prev_task_rt
>  => pick_next_task_idle

So we'll go idle, but as of this point we're still running the rt task.

So your Changelog is actively wrong, the tasks _are_ still running,
albeit not for very much longer.