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Groups > linux.kernel > #1423128
| From | "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [patch 00/20] timer: Refactor the timer wheel |
| Date | 2016-06-15 17:20 +0200 |
| Message-ID | <rKkLL-4en-5@gated-at.bofh.it> (permalink) |
| References | <rJvJf-3OU-5@gated-at.bofh.it> <rJCKK-eX-17@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On Mon, Jun 13, 2016 at 09:15:14AM -0700, Paul E. McKenney wrote:
> On Mon, Jun 13, 2016 at 08:40:50AM -0000, Thomas Gleixner wrote:
> > The current timer wheel has some drawbacks:
> >
> > 1) Cascading
> >
> > Cascading can be an unbound operation and is completely pointless in most
> > cases because the vast majority of the timer wheel timers are canceled or
> > rearmed before expiration.
> >
> > 2) No fast lookup of the next expiring timer
> >
> > In NOHZ scenarios the first timer soft interrupt after a long NOHZ period
> > must fast forward the base time to current jiffies. As we have no way to
> > find the next expiring timer fast, the code loops and increments the base
> > time by one and checks for expired timers in each step. I've observed loops
> > lasting 1 ms!
> >
> > There are some other issues caused by the above, but they are minor compare to
> > those.
>
> For SMP configurations, this passes light rcutorture testing. For UP
> builds, it complains about undefined symbols. Builds succeed with
> the following kneejerk patch. Am retesting rcutorture.
And with the patch below, testing goes as well with your patch stack as
it does without it. So, with that patch (or equivalent):
Tested-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
There were some complaints about increasing the size of the tiny
configuration, FYI.
So, just out of curiosity, does anyone still run -rt on single-CPU systems?
Thanx, Paul
> ------------------------------------------------------------------------
>
> commit 87dbd35cf4034f2b664b6e9d60decd2bdbfc416f
> Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> Date: Mon Jun 13 09:11:41 2016 -0700
>
> Fix undefined get_nohz_timer_target() in non-SMP builds
>
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 6e42ada26345..322e52415a29 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -348,6 +348,10 @@ extern int get_nohz_timer_target(void);
> #else
> static inline void nohz_balance_enter_idle(int cpu) { }
> static inline void set_cpu_sd_state_idle(void) { }
> +static inline int get_nohz_timer_target(void)
> +{
> + return raw_smp_processor_id();
> +}
> #endif
>
> /*
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[patch 00/20] timer: Refactor the timer wheel Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 10:50 +0200
[patch 11/20] hlist: Add hlist_is_last_node() helper Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 10:50 +0200
Re: [patch 11/20] hlist: Add hlist_is_last_node() helper Paolo Bonzini <pbonzini@redhat.com> - 2016-06-13 12:30 +0200
[patch 07/20] drivers/tty/mips_ejtag: Initialize timer as pinned Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 10:50 +0200
[patch 01/20] timer: Make pinned a timer property Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 10:50 +0200
[patch 17/20] tick/sched: Remove pointless empty function Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 10:50 +0200
[patch 05/20] driver/net/ethernet/tile: Initialize timer as pinned Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 10:50 +0200
[patch 15/20] timer: Move __run_timers() function Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 10:50 +0200
[patch 12/20] timer: Give a few structs and members proper names Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 10:50 +0200
[patch 04/20] cpufreq/powernv: Initialize timer as pinned Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 10:50 +0200
Re: [patch 04/20] cpufreq/powernv: Initialize timer as pinned Arjan van de Ven <arjanvandeven@gmail.com> - 2016-06-13 15:20 +0200
[patch 13/20] timer: Switch to a non cascading wheel Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 10:50 +0200
Re: [patch 13/20] timer: Switch to a non cascading wheel Peter Zijlstra <peterz@infradead.org> - 2016-06-13 13:50 +0200
Re: [patch 13/20] timer: Switch to a non cascading wheel Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 14:40 +0200
Re: [patch 13/20] timer: Switch to a non cascading wheel Eric Dumazet <edumazet@google.com> - 2016-06-13 14:50 +0200
Re: [patch 13/20] timer: Switch to a non cascading wheel Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 16:40 +0200
Re: [patch 13/20] timer: Switch to a non cascading wheel Ingo Molnar <mingo@kernel.org> - 2016-06-14 12:20 +0200
Re: [patch 13/20] timer: Switch to a non cascading wheel Thomas Gleixner <tglx@linutronix.de> - 2016-06-14 18:40 +0200
Re: [patch 13/20] timer: Switch to a non cascading wheel Arjan van de Ven <arjanvandeven@gmail.com> - 2016-06-14 19:20 +0200
Re: [patch 13/20] timer: Switch to a non cascading wheel Thomas Gleixner <tglx@linutronix.de> - 2016-06-14 20:10 +0200
Re: [patch 13/20] timer: Switch to a non cascading wheel Peter Zijlstra <peterz@infradead.org> - 2016-06-14 22:40 +0200
Re: [patch 13/20] timer: Switch to a non cascading wheel Peter Zijlstra <peterz@infradead.org> - 2016-06-14 22:50 +0200
Re: [patch 13/20] timer: Switch to a non cascading wheel Eric Dumazet <edumazet@google.com> - 2016-06-14 23:20 +0200
Re: [patch 13/20] timer: Switch to a non cascading wheel Thomas Gleixner <tglx@linutronix.de> - 2016-06-15 17:00 +0200
Re: [patch 13/20] timer: Switch to a non cascading wheel Arjan van de Ven <arjanvandeven@gmail.com> - 2016-06-15 17:00 +0200
Re: [patch 13/20] timer: Switch to a non cascading wheel Thomas Gleixner <tglx@linutronix.de> - 2016-06-15 18:50 +0200
Re: [patch 13/20] timer: Switch to a non cascading wheel Thomas Gleixner <tglx@linutronix.de> - 2016-06-16 17:50 +0200
Re: [patch 13/20] timer: Switch to a non cascading wheel "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-06-16 18:10 +0200
Re: [patch 13/20] timer: Switch to a non cascading wheel Peter Zijlstra <peterz@infradead.org> - 2016-06-16 20:20 +0200
Re: [patch 13/20] timer: Switch to a non cascading wheel "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-06-17 02:50 +0200
Re: [patch 13/20] timer: Switch to a non cascading wheel "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-06-17 06:10 +0200
Re: [patch 13/20] timer: Switch to a non cascading wheel Arjan van de Ven <arjanvandeven@gmail.com> - 2016-06-16 18:10 +0200
Re: [patch 13/20] timer: Switch to a non cascading wheel Thomas Gleixner <tglx@linutronix.de> - 2016-06-16 18:20 +0200
Re: [patch 13/20] timer: Switch to a non cascading wheel Eric Dumazet <edumazet@google.com> - 2016-06-15 17:10 +0200
Re: [patch 13/20] timer: Switch to a non cascading wheel Richard Cochran <richardcochran@gmail.com> - 2016-06-13 16:40 +0200
Re: [patch 13/20] timer: Switch to a non cascading wheel Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 16:50 +0200
[patch 14/20] timer: Remove slack leftovers Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 10:50 +0200
[patch 18/20] timer: Forward wheel clock whenever possible Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 10:50 +0200
Re: [patch 18/20] timer: Forward wheel clock whenever possible Richard Cochran <richardcochran@gmail.com> - 2016-06-13 17:20 +0200
Re: [patch 18/20] timer: Forward wheel clock whenever possible Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 17:30 +0200
[patch 06/20] drivers/tty/metag_da: Initialize timer as pinned Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 11:00 +0200
Re: [patch 06/20] drivers/tty/metag_da: Initialize timer as pinned Arjan van de Ven <arjanvandeven@gmail.com> - 2016-06-13 15:20 +0200
[patch 03/20] x86/mce: Initialize timer as pinned Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 11:00 +0200
[patch 08/20] net/ipv4/inet: Initialize timers as pinned Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 11:00 +0200
[patch 02/20] x86/apic/uv: Initialize timer as pinned Thomas Gleixner <tglx@linutronix.de> - 2016-06-13 11:00 +0200
Re: [patch 00/20] timer: Refactor the timer wheel Eric Dumazet <edumazet@google.com> - 2016-06-13 16:20 +0200
Re: [patch 00/20] timer: Refactor the timer wheel "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-06-13 18:20 +0200
Re: [patch 00/20] timer: Refactor the timer wheel "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-06-15 17:20 +0200
Re: [patch 00/20] timer: Refactor the timer wheel Thomas Gleixner <tglx@linutronix.de> - 2016-06-15 19:10 +0200
Re: [patch 00/20] timer: Refactor the timer wheel "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2016-06-15 22:30 +0200
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