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From:   John Ogness <john.ogness@linutronix.de>
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To:     Gautam Thaker <ghthaker@gmail.com>, linux-rt-users@vger.kernel.org
Subject: Re: 5.15.28-rt35 #2 SMP PREEMPT_RT: Should scheduling latency be as
 large as 800 usec?
In-Reply-To: <CA+1+E3UVmbLA76t_JkZMMC6FHsmc_EOKeLztvgN6nAhTjjK5bQ@mail.gmail.com>
References: <CA+1+E3UVmbLA76t_JkZMMC6FHsmc_EOKeLztvgN6nAhTjjK5bQ@mail.gmail.com>
Date:   Wed, 23 Mar 2022 21:09:53 +0106
Message-ID: <871qyse8ra.fsf@jogness.linutronix.de>
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On 2022-03-23, Gautam Thaker <ghthaker@gmail.com> wrote:
> I built 5.15.28-rt35 #2 SMP PREEMPT_RT  with  =E2=80=9CFully Preemptible
> Kernel" option and otherwise using .config from  a stock Ubuntu 20.04
>  5.4.0 kernel.
>
> Quick question: I see scheduling/wake_up latencies around 800 usec and
> this is confirmed by cyclictest.
[...]
> node-0> grep -i preempt /boot/config-5.15.28-rt35
> node-0> grep -i debug  /boot/config-5.15.28-rt35 |grep  =3Dy
[...]
> processor       : 31
> vendor_id       : GenuineIntel
> cpu family      : 6
> model           : 63
> model name      : Intel(R) Xeon(R) CPU E5-2630 v3 @ 2.40GHz
> stepping        : 2
> microcode       : 0x46
> cpu MHz         : 1200.000
> cache size      : 20480 KB

Your CPU is running at 1.2GHz although it is capable of 2.4GHz. This
looks like you have CPU frequency scaling activated. Investigate:

grep -i cpu_freq /boot/config-5.15.28-rt35

The configuration of your tick may also be interesting:

grep -i hz /boot/config-5.15.28-rt35

John Ogness