linux-kernel - Re: [PATCH 3/3] LoongArch: Allow to enable PREEMPT

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Message-ID: <CAAhV-H4ecBZsV+9SxLZ-JFiUK=b3tMqkLZe0djac0_390==MMw@mail.gmail.com>
Date: Thu, 14 Nov 2024 19:19:26 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: Huacai Chen <chenhuacai@...ngson.cn>, Xuerui Wang <kernel@...0n.name>, loongarch@...ts.linux.dev, 
	Clark Williams <clrkwllms@...nel.org>, Steven Rostedt <rostedt@...dmis.org>, 
	linux-rt-devel@...ts.linux.dev, Guo Ren <guoren@...nel.org>, 
	Jiaxun Yang <jiaxun.yang@...goat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] LoongArch: Allow to enable PREEMPT_RT

On Thu, Nov 14, 2024 at 7:14 PM Sebastian Andrzej Siewior
<bigeasy@...utronix.de> wrote:
>
> On 2024-11-14 19:07:37 [+0800], Huacai Chen wrote:
> > Hi, Sebastian,
> Hi,
>
> > > Why is ntpd/chronyd service affecting this? Is it running at prio 99?
> > > Otherwise it should not be noticed.
> > No, ntpd/chronyd doesn't affect latency. But they may trigger RTC
> > synchronization every 11 minutes, and RTC synchronization affects
> > latency. We can keep ntpd/chronyd running but disable RTC
> > synchronization by configuration, this is the least aggressive method.
>
> What is "RTC synchronization" in this context?
Means the sync_hw_clock() function in kernel/time/ntp.c, it can be
enabled/disabled by chronyd configuration:

/etc/chrony.conf
# Enable kernel synchronization of the real-time clock (RTC).
# rtcsync

Huacai

>
> > > Is lockdep complaining in any workloads?
> > > Is CONFIG_DEBUG_ATOMIC_SLEEP leading to any complains?
> > This needs more tests because I haven't enabled them.
>
> That would be good. It would show if there is anything that has not yet
> been noticed.
>
> > Huacai
>
> Sebastian