From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Eric Dumazet <edumazet@google.com>,
Frederic Weisbecker <fweisbec@gmail.com>,
Chris Mason <clm@fb.com>, Arjan van de Ven <arjan@infradead.org>,
rt@linutronix.de
Subject: Re: [patch 00/20] timer: Refactor the timer wheel
Date: Mon, 13 Jun 2016 09:15:14 -0700 [thread overview]
Message-ID: <20160613161514.GA3923@linux.vnet.ibm.com> (raw)
In-Reply-To: <20160613070440.950649741@linutronix.de>
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.
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
/*
next prev parent reply other threads:[~2016-06-13 16:15 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-13 8:40 [patch 00/20] timer: Refactor the timer wheel Thomas Gleixner
2016-06-13 8:40 ` [patch 01/20] timer: Make pinned a timer property Thomas Gleixner
2016-06-13 8:40 ` [patch 02/20] x86/apic/uv: Initialize timer as pinned Thomas Gleixner
2016-06-13 8:40 ` [patch 03/20] x86/mce: " Thomas Gleixner
2016-06-13 8:40 ` [patch 04/20] cpufreq/powernv: " Thomas Gleixner
2016-06-13 13:18 ` Arjan van de Ven
2016-06-13 8:40 ` [patch 05/20] driver/net/ethernet/tile: " Thomas Gleixner
2016-06-13 8:40 ` [patch 06/20] drivers/tty/metag_da: " Thomas Gleixner
2016-06-13 13:13 ` Arjan van de Ven
2016-06-13 8:40 ` [patch 07/20] drivers/tty/mips_ejtag: " Thomas Gleixner
2016-06-13 8:40 ` [patch 08/20] net/ipv4/inet: Initialize timers " Thomas Gleixner
2016-06-13 8:40 ` [patch 09/20] timer: Remove mod_timer_pinned Thomas Gleixner
2016-06-13 8:40 ` [patch 10/20] timer: Add a cascading tracepoint Thomas Gleixner
2016-06-13 8:40 ` [patch 11/20] hlist: Add hlist_is_last_node() helper Thomas Gleixner
2016-06-13 10:27 ` Paolo Bonzini
2016-06-13 8:40 ` [patch 12/20] timer: Give a few structs and members proper names Thomas Gleixner
2016-06-13 8:41 ` [patch 13/20] timer: Switch to a non cascading wheel Thomas Gleixner
2016-06-13 11:40 ` Peter Zijlstra
2016-06-13 12:30 ` Thomas Gleixner
2016-06-13 12:46 ` Eric Dumazet
2016-06-13 14:30 ` Thomas Gleixner
2016-06-14 10:11 ` Ingo Molnar
2016-06-14 16:28 ` Thomas Gleixner
2016-06-14 17:14 ` Arjan van de Ven
2016-06-14 18:05 ` Thomas Gleixner
2016-06-14 20:34 ` Peter Zijlstra
2016-06-14 20:42 ` Peter Zijlstra
2016-06-14 21:17 ` Eric Dumazet
2016-06-15 14:53 ` Thomas Gleixner
2016-06-15 14:55 ` Arjan van de Ven
2016-06-15 16:43 ` Thomas Gleixner
2016-06-16 15:43 ` Thomas Gleixner
2016-06-16 16:02 ` Paul E. McKenney
2016-06-16 18:14 ` Peter Zijlstra
2016-06-17 0:40 ` Paul E. McKenney
2016-06-17 4:04 ` Paul E. McKenney
2016-06-16 16:04 ` Arjan van de Ven
2016-06-16 16:09 ` Thomas Gleixner
2016-06-15 15:05 ` Eric Dumazet
2016-06-13 14:36 ` Richard Cochran
2016-06-13 14:39 ` Thomas Gleixner
2016-06-13 8:41 ` [patch 15/20] timer: Move __run_timers() function Thomas Gleixner
2016-06-13 8:41 ` [patch 14/20] timer: Remove slack leftovers Thomas Gleixner
2016-06-13 8:41 ` [patch 16/20] timer: Optimize collect timers for NOHZ Thomas Gleixner
2016-06-13 8:41 ` [patch 17/20] tick/sched: Remove pointless empty function Thomas Gleixner
2016-06-13 8:41 ` [patch 18/20] timer: Forward wheel clock whenever possible Thomas Gleixner
2016-06-13 15:14 ` Richard Cochran
2016-06-13 15:18 ` Thomas Gleixner
2016-06-13 8:41 ` [patch 19/20] timer: Split out index calculation Thomas Gleixner
2016-06-13 8:41 ` [patch 20/20] timer: Optimization for same expiry time in mod_timer() Thomas Gleixner
2016-06-13 14:10 ` [patch 00/20] timer: Refactor the timer wheel Eric Dumazet
2016-06-13 16:15 ` Paul E. McKenney [this message]
2016-06-15 15:15 ` Paul E. McKenney
2016-06-15 17:02 ` Thomas Gleixner
2016-06-15 20:26 ` Paul E. McKenney
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