linux-kernel - Re: [RFC PATCH] cpufreq: qcom-cpufreq-hw: allow work to be done on other CPU for PREEMPT

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Message-ID: <a0e1b3b9-b333-e0ac-ac46-c15a01b356e6@linaro.org>
Date:   Fri, 17 Mar 2023 09:13:42 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Hillf Danton <hdanton@...a.com>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        linux-arm-msm@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Adrien Thierry <athierry@...hat.com>,
        Brian Masney <bmasney@...hat.com>,
        linux-rt-users@...r.kernel.org
Subject: Re: [RFC PATCH] cpufreq: qcom-cpufreq-hw: allow work to be done on
 other CPU for PREEMPT_RT

On 17/03/2023 00:57, Hillf Danton wrote:
> On 16 Mar 2023 13:28:18 +0100 Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
>> On 15/03/2023 17:49, Krzysztof Kozlowski wrote:
>>> Qualcomm cpufreq driver configures interrupts with affinity to each
>>> cluster, e.g.  dcvsh-irq-0, dcvsh-irq-4 and dcvsh-irq-7 on SM8250.
>>> Triggered interrupt will schedule delayed work, but, since workqueue
>>> prefers local CPUs, it might get executed on a CPU dedicated to realtime
>>> tasks causing unexpected latencies in realtime workload.
>>>
>>> Use unbound workqueue for such case.  This might come with performance
>>> or energy penalty, e.g. because of cache miss or when other CPU is
>>> sleeping.
>>>
>>> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
>>> ---
>>>  drivers/cpufreq/qcom-cpufreq-hw.c | 11 ++++++++++-
>>
>> Let me also paste impact of this patch - rtla osnoise on entirely idle
>> system (cores 2-7 isolated for Realtime):
> 
> Are cores 2-7 the non-housekeeping CPUs[1]?

Yes, since their are isolated for Realtime this is synonymous.

> 
> [1] https://lore.kernel.org/lkml/20230223150624.GA29739@lst.de/



Best regards,
Krzysztof