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Date:   Fri, 11 Aug 2023 11:17:19 -0400
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Atul Pant <quic_atulpant@quicinc.com>
Cc:     rafael@kernel.org, daniel.lezcano@linaro.org, mingo@redhat.com,
        peterz@infradead.org, juri.lelli@redhat.com,
        vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
        bsegall@google.com, mgorman@suse.de, bristot@redhat.com,
        vschneid@redhat.com, linux-pm@vger.kernel.org,
        linux-kernel@vger.kernel.org, quic_ashayj@quicinc.com,
        quic_rgottimu@quicinc.com, quic_shashim@quicinc.com
Subject: Re: Prevent RT-throttling for idle-injection threads
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On Tue,  8 Aug 2023 16:55:23 +0530
Atul Pant <quic_atulpant@quicinc.com> wrote:

> Hi all,
> We are trying to implement a solution for thermal mitigation by using
> idle injection on CPUs. However we face some limitations with the current
> idle-inject framework. As per our need, we want to start injecting idle
> cycles on a CPU for indefinite time (until the temperature/power of the
> CPU falls below a threshold). This will help to keep the hot CPUs in the
> sleep state until we see improvement in temperature/power. If we set the
> idle duration to a large value or have an idle-injection ratio of 100%,
> then the idle-inject RT thread suffers from RT throttling. This results
> in the CPU exiting from the sleep state and consuming some power.
> 
> The above situation can be avoided, if we can prevent RT throttling on
> the injected CPU. With the currently available sysctl parameters,
> sched_rt_runtime_us and sched_rt_period_us, we can prevent RT throttling
> by either setting sched_rt_runtime_us equal to sched_rt_period_us or,
> setting sched_rt_runtime_us to -1. Since these parameters are system
> wide, so it will affect the RT tasks on non idle-injected CPUs as well.
> To overcome this, will it be feasible to have these two parameters on a
> per CPU basis? This will allow to selectively disable RT throttling on
> idle-injected CPUs.

I wonder if the deadline scheduler that Daniel is working on would help in this case?

-- Steve