From: Zhouyi Zhou <zhouzhouyi@gmail.com>
To: Frederic Weisbecker <frederic@kernel.org>
Cc: dave@stgolabs.net, paulmck@kernel.org, fweisbec@gmail.com,
josh@joshtriplett.org, linux-kernel@vger.kernel.org,
tglx@linutronix.de, linuxppc-dev@lists.ozlabs.org,
mingo@kernel.org
Subject: Re: [PATCH linux-next][RFC]torture: avoid offline tick_do_timer_cpu
Date: Thu, 24 Nov 2022 10:18:51 +0800 [thread overview]
Message-ID: <CAABZP2yDMTKqkj6r+hsQb=3zdoXOWMQ8Z3QKSxaaVTWv2eS-kw@mail.gmail.com> (raw)
In-Reply-To: <20221123223658.GC1395324@lothringen>
On Thu, Nov 24, 2022 at 6:37 AM Frederic Weisbecker <frederic@kernel.org> wrote:
>
> On Mon, Nov 21, 2022 at 11:51:40AM +0800, Zhouyi Zhou wrote:
> > During CPU-hotplug torture (CONFIG_NO_HZ_FULL=y), if we try to
> > offline tick_do_timer_cpu, the operation will fail because in
> > function tick_nohz_cpu_down:
> > ```
> > if (tick_nohz_full_running && tick_do_timer_cpu == cpu)
> > return -EBUSY;
> > ```
> > Above bug was first discovered in torture tests performed in PPC VM
> > of Open Source Lab of Oregon State University, and reproducable in RISC-V
> > and X86-64 (with additional kernel commandline cpu0_hotplug).
> >
> > In this patch, we avoid offline tick_do_timer_cpu by distribute
> > the offlining cpu among remaining cpus.
> >
> > Signed-off-by: Zhouyi Zhou <zhouzhouyi@gmail.com>
> > ---
> > include/linux/tick.h | 1 +
> > kernel/time/tick-common.c | 1 +
> > kernel/time/tick-internal.h | 1 -
> > kernel/torture.c | 10 ++++++++++
> > 4 files changed, 12 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/linux/tick.h b/include/linux/tick.h
> > index bfd571f18cfd..23cc0b205853 100644
> > --- a/include/linux/tick.h
> > +++ b/include/linux/tick.h
> > @@ -14,6 +14,7 @@
> > #include <linux/rcupdate.h>
> >
> > #ifdef CONFIG_GENERIC_CLOCKEVENTS
> > +extern int tick_do_timer_cpu __read_mostly;
> > extern void __init tick_init(void);
> > /* Should be core only, but ARM BL switcher requires it */
> > extern void tick_suspend_local(void);
> > diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
> > index 46789356f856..87b9b9afa320 100644
> > --- a/kernel/time/tick-common.c
> > +++ b/kernel/time/tick-common.c
> > @@ -48,6 +48,7 @@ ktime_t tick_next_period;
> > * procedure also covers cpu hotplug.
> > */
> > int tick_do_timer_cpu __read_mostly = TICK_DO_TIMER_BOOT;
> > +EXPORT_SYMBOL_GPL(tick_do_timer_cpu);
>
> Please rather make a function for this. This is an internal value
> that we don't want to expose to modules.
>
> This can be:
>
> int tick_nohz_full_timekeeper(void)
> {
> if (tick_nohz_full_enabled() && tick_do_timer_cpu >= 0)
> return tick_do_timer_cpu;
> else
> return nr_cpu_ids;
> }
>
> And then just check if the value is below nr_cpu_ids.
Thank Paul and Frederic both for your guidance!
Things are much easier;-) and I will do it.
Cheers
Zhouyi
>
> Thanks.
next prev parent reply other threads:[~2022-11-24 2:20 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-21 3:51 [PATCH linux-next][RFC]torture: avoid offline tick_do_timer_cpu Zhouyi Zhou
2022-11-22 1:37 ` Paul E. McKenney
2022-11-23 2:23 ` Zhouyi Zhou
2022-11-23 18:49 ` Paul E. McKenney
2022-11-24 2:35 ` Zhouyi Zhou
2022-11-23 22:25 ` Frederic Weisbecker
2022-11-23 23:00 ` Paul E. McKenney
2022-11-23 22:36 ` Frederic Weisbecker
2022-11-24 2:18 ` Zhouyi Zhou [this message]
2022-11-26 17:05 ` Thomas Gleixner
2022-11-27 2:45 ` Zhouyi Zhou
2022-11-27 12:40 ` Thomas Gleixner
2022-11-27 17:53 ` Paul E. McKenney
2022-11-28 3:00 ` Zhouyi Zhou
2022-11-28 8:12 ` Thomas Gleixner
2022-11-28 15:16 ` Paul E. McKenney
2023-07-06 7:09 ` Christophe Leroy
2023-07-06 8:13 ` Zhouyi Zhou
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CAABZP2yDMTKqkj6r+hsQb=3zdoXOWMQ8Z3QKSxaaVTWv2eS-kw@mail.gmail.com' \
--to=zhouzhouyi@gmail.com \
--cc=dave@stgolabs.net \
--cc=frederic@kernel.org \
--cc=fweisbec@gmail.com \
--cc=josh@joshtriplett.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=mingo@kernel.org \
--cc=paulmck@kernel.org \
--cc=tglx@linutronix.de \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).