From: Zhouyi Zhou <zhouzhouyi@gmail.com> To: Frederic Weisbecker <frederic@kernel.org> Cc: fweisbec@gmail.com, tglx@linutronix.de, mingo@kernel.org, dave@stgolabs.net, paulmck@kernel.org, josh@joshtriplett.org, mpe@ellerman.id.au, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.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.
WARNING: multiple messages have this Message-ID (diff)
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 2:19 UTC|newest] Thread overview: 33+ 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 2022-11-22 1:37 ` Paul E. McKenney 2022-11-23 2:23 ` Zhouyi Zhou 2022-11-23 2:23 ` Zhouyi Zhou 2022-11-23 18:49 ` Paul E. McKenney 2022-11-23 18:49 ` Paul E. McKenney 2022-11-24 2:35 ` Zhouyi Zhou 2022-11-24 2:35 ` Zhouyi Zhou 2022-11-23 22:25 ` Frederic Weisbecker 2022-11-23 22:25 ` Frederic Weisbecker 2022-11-23 23:00 ` Paul E. McKenney 2022-11-23 23:00 ` Paul E. McKenney 2022-11-23 22:36 ` Frederic Weisbecker 2022-11-23 22:36 ` Frederic Weisbecker 2022-11-24 2:18 ` Zhouyi Zhou [this message] 2022-11-24 2:18 ` Zhouyi Zhou 2022-11-26 17:05 ` Thomas Gleixner 2022-11-27 2:45 ` Zhouyi Zhou 2022-11-27 2:45 ` Zhouyi Zhou 2022-11-27 12:40 ` Thomas Gleixner 2022-11-27 12:40 ` Thomas Gleixner 2022-11-27 17:53 ` Paul E. McKenney 2022-11-27 17:53 ` Paul E. McKenney 2022-11-28 3:00 ` Zhouyi Zhou 2022-11-28 3:00 ` Zhouyi Zhou 2022-11-28 8:12 ` Thomas Gleixner 2022-11-28 8:12 ` Thomas Gleixner 2022-11-28 15:16 ` Paul E. McKenney 2022-11-28 15:16 ` Paul E. McKenney 2023-07-06 7:09 ` Christophe Leroy 2023-07-06 8:13 ` Zhouyi Zhou 2023-07-06 8:13 ` Zhouyi Zhou
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