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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAAhV-H4jDNG8nsW30U9zE1-c6dHwy2fSjy5hkZhpWWu3=og64A@mail.gmail.com>
Date: Thu, 14 Nov 2024 19:36:38 +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 7:30 PM Sebastian Andrzej Siewior
<bigeasy@...utronix.de> wrote:
>
> On 2024-11-14 19:19:26 [+0800], Huacai Chen wrote:
> > > > > 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:
>
> But what exactly is sync_hw_clock() doing that is causing a problem
> here? The clock on HW is updated. The access to the RTC clock is
> preemptible.
This is a platform-specific problem, our RTC driver is
drivers/rtc/rtc-loongson.c, the write operation to RTC register is
slow.

Huacai

>
> > Huacai
>
> Sebastian
>