linux-kernel - Re: [RFC 1/4] sched/core: Introduce per_cpu counter to track latency sensitive tasks

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Message-ID: <20200508084002.GK19464@codeaurora.org>
Date:   Fri, 8 May 2020 14:10:02 +0530
From:   Pavan Kondeti <pkondeti@...eaurora.org>
To:     Parth Shah <parth@...ux.ibm.com>
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        mingo@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, qais.yousef@....com,
        chris.hyser@...cle.com, valentin.schneider@....com,
        rjw@...ysocki.net
Subject: Re: [RFC 1/4] sched/core: Introduce per_cpu counter to track latency
 sensitive tasks

On Thu, May 07, 2020 at 07:07:20PM +0530, Parth Shah wrote:
> The "nr_lat_sensitive" per_cpu variable provides hints on the possible
> number of latency-sensitive tasks occupying the CPU. This hints further
> helps in inhibiting the CPUIDLE governor from calling deeper IDLE states
> (next patches includes this).
> 

Can you please explain the intended use case here? Once a latency sensitive
task is created, it prevents c-state on a CPU whether the task runs again
or not in the near future.

I assume, either these latency sensitive tasks won't be around for long time
or applications set/reset latency sensitive nice value dynamically.

Thanks,
Pavan
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