From: Frederic Weisbecker <fweisbec@gmail.com>
To: Christoph Lameter <cl@linux.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
linaro-sched-sig@lists.linaro.org,
Alessio Igor Bogani <abogani@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Avi Kivity <avi@redhat.com>, Chris Metcalf <cmetcalf@tilera.com>,
Daniel Lezcano <daniel.lezcano@linaro.org>,
Geoff Levand <geoff@infradead.org>,
Gilad Ben Yossef <gilad@benyossef.com>,
Ingo Molnar <mingo@kernel.org>,
Max Krasnyansky <maxk@qualcomm.com>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Peter Zijlstra <peterz@infradead.org>,
Stephen Hemminger <shemminger@vyatta.com>,
Steven Rostedt <rostedt@goodmis.org>,
Sven-Thorsten Dietrich <thebigcorporation@gmail.com>,
Thomas Gleixner <tglx@linutronix.de>,
Zen Lin <zen@openhuawei.org>
Subject: Re: [PATCH 11/32] nohz/cpuset: Don't turn off the tick if rcu needs it
Date: Wed, 28 Mar 2012 13:53:07 +0200 [thread overview]
Message-ID: <20120328115304.GC17189@somewhere.redhat.com> (raw)
In-Reply-To: <alpine.DEB.2.00.1203271111110.1170@router.home>
On Tue, Mar 27, 2012 at 11:13:39AM -0500, Christoph Lameter wrote:
> On Tue, 27 Mar 2012, Frederic Weisbecker wrote:
>
> > > Is there any way for userspace to know that the tick is not off yet due to
> > > this? It would make sense for us to have busy loop in user space that
> > > waits until the OS has completed all processing if that avoids future
> > > latencies for the application.
> >
> > What is the usecase you have in mind? Is it for realtime purpose?
>
> Please do not use "realtime" since I am not sure what you mean by that.
> Its for a low latency applications that cannot use "realtime" because that
> implies high latencies.
>
> > The "tick stopped" is a volatile and relative state.
>
> The use case is an application that cannot tolerate the latencies
> introduced by timer tick processing. It will only start running when the
> system is in a sufficiently quiet state.
>
> > Relative because if a timer list is enqueued to fire 1 second later,
> > the tick will be stopped until that happens. How do we consider this (common)
> > case?
> >
> > Also as Chris noted it is volatile because the tick can be restarted anytime
> > for random reasons: the CPU receives an IPI which makes it restart the
> > periodic tick.
>
> Ok some sort of notification would be good for that case. If a timer tick
> happens and that was unavoidable then it would be good to log the reason
> why this occured so that the system can be configured in such a way that
> these interruptions are minimized.
tracing is probably the right place to log these things. But that's
about debugging. This won't be a notification on top of which your app
could recover.
next prev parent reply other threads:[~2012-03-28 11:53 UTC|newest]
Thread overview: 96+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-03-21 13:58 [RFC][PATCH 00/32] Nohz cpusets v2 (adaptive tickless kernel) Frederic Weisbecker
2012-03-21 13:58 ` Frederic Weisbecker
2012-04-04 15:33 ` warning in tick_nohz_irq_exit Stephen Hemminger
2012-04-04 20:45 ` Frederic Weisbecker
2012-03-21 13:58 ` [PATCH 01/32] nohz: Separate idle sleeping time accounting from nohz logic Frederic Weisbecker
2012-03-21 13:58 ` [PATCH 02/32] nohz: Make nohz API agnostic against idle ticks cputime accounting Frederic Weisbecker
2012-03-21 13:58 ` [PATCH 03/32] nohz: Rename ts->idle_tick to ts->last_tick Frederic Weisbecker
2012-03-21 13:58 ` [PATCH 04/32] nohz: Move nohz load balancer selection into idle logic Frederic Weisbecker
2012-03-21 13:58 ` [PATCH 05/32] nohz: Move ts->idle_calls incrementation into strict " Frederic Weisbecker
2012-03-21 13:58 ` [PATCH 06/32] nohz: Move next idle expiry time record into idle logic area Frederic Weisbecker
2012-03-21 13:58 ` [PATCH 07/32] cpuset: Set up interface for nohz flag Frederic Weisbecker
2012-03-21 14:50 ` Christoph Lameter
2012-03-22 4:03 ` Mike Galbraith
2012-03-22 16:26 ` Christoph Lameter
2012-03-22 19:20 ` Mike Galbraith
2012-03-27 11:22 ` Frederic Weisbecker
2012-03-27 11:53 ` Mike Galbraith
2012-03-27 11:56 ` Frederic Weisbecker
2012-03-27 12:31 ` Mike Galbraith
2012-03-27 11:19 ` Frederic Weisbecker
2012-03-21 13:58 ` [PATCH 08/32] nohz: Try not to give the timekeeping duty to an adaptive tickless cpu Frederic Weisbecker
2012-03-21 14:52 ` Christoph Lameter
2012-03-27 10:50 ` Frederic Weisbecker
2012-03-27 16:08 ` Christoph Lameter
2012-03-27 16:47 ` Peter Zijlstra
2012-03-28 1:12 ` Christoph Lameter
2012-03-28 8:39 ` Peter Zijlstra
2012-03-28 13:11 ` Dimitri Sivanich
2012-03-28 15:51 ` Chris Metcalf
2012-03-30 1:34 ` Frederic Weisbecker
2012-03-21 13:58 ` [PATCH 09/32] x86: New cpuset nohz irq vector Frederic Weisbecker
2012-03-21 13:58 ` [PATCH 10/32] nohz: Adaptive tick stop and restart on nohz cpuset Frederic Weisbecker
2012-03-21 13:58 ` [PATCH 11/32] nohz/cpuset: Don't turn off the tick if rcu needs it Frederic Weisbecker
2012-03-21 14:54 ` Christoph Lameter
2012-03-22 7:38 ` Gilad Ben-Yossef
2012-03-22 16:18 ` Christoph Lameter
2012-03-27 15:21 ` Gilad Ben-Yossef
2012-03-28 12:39 ` Frederic Weisbecker
2012-03-28 12:57 ` Gilad Ben-Yossef
2012-03-28 13:38 ` Frederic Weisbecker
2012-03-22 17:18 ` Chris Metcalf
2012-03-27 15:31 ` Gilad Ben-Yossef
2012-03-27 15:43 ` Chris Metcalf
2012-03-28 8:36 ` Gilad Ben-Yossef
2012-03-27 12:13 ` Frederic Weisbecker
2012-03-27 16:13 ` Christoph Lameter
2012-03-27 16:24 ` Steven Rostedt
2012-03-28 0:42 ` Christoph Lameter
2012-03-28 1:06 ` Steven Rostedt
2012-03-28 1:19 ` Christoph Lameter
2012-03-28 1:35 ` Steven Rostedt
2012-03-28 3:17 ` Steven Rostedt
2012-03-28 7:55 ` Gilad Ben-Yossef
2012-03-28 12:21 ` Frederic Weisbecker
2012-03-28 12:41 ` Gilad Ben-Yossef
2012-03-28 14:02 ` Steven Rostedt
2012-03-28 11:53 ` Frederic Weisbecker [this message]
2012-03-21 13:58 ` [PATCH 12/32] nohz/cpuset: Wake up adaptive nohz CPU when a timer gets enqueued Frederic Weisbecker
2012-03-21 13:58 ` [PATCH 13/32] nohz/cpuset: Don't stop the tick if posix cpu timers are running Frederic Weisbecker
2012-03-21 13:58 ` [PATCH 14/32] nohz/cpuset: Restart tick when nohz flag is cleared on cpuset Frederic Weisbecker
2012-03-21 13:58 ` [PATCH 15/32] nohz/cpuset: Restart the tick if printk needs it Frederic Weisbecker
2012-03-21 13:58 ` [PATCH 16/32] rcu: Restart the tick on non-responding adaptive nohz CPUs Frederic Weisbecker
2012-03-21 13:58 ` [PATCH 17/32] rcu: Restart tick if we enqueue a callback in a nohz/cpuset CPU Frederic Weisbecker
2012-03-21 13:58 ` [PATCH 18/32] nohz: Generalize tickless cpu time accounting Frederic Weisbecker
2012-03-21 13:58 ` [PATCH 19/32] nohz/cpuset: Account user and system times in adaptive nohz mode Frederic Weisbecker
2012-03-21 13:58 ` [PATCH 20/32] nohz/cpuset: New API to flush cputimes on nohz cpusets Frederic Weisbecker
2012-03-21 13:58 ` [PATCH 21/32] nohz/cpuset: Flush cputime on threads in nohz cpusets when waiting leader Frederic Weisbecker
2012-03-27 14:10 ` Gilad Ben-Yossef
2012-03-27 14:23 ` Gilad Ben-Yossef
2012-03-28 11:20 ` Frederic Weisbecker
2012-03-21 13:58 ` [PATCH 22/32] nohz/cpuset: Flush cputimes on procfs stat file read Frederic Weisbecker
2012-03-21 13:58 ` [PATCH 23/32] nohz/cpuset: Flush cputimes for getrusage() and times() syscalls Frederic Weisbecker
2012-03-21 13:58 ` [PATCH 24/32] x86: Syscall hooks for nohz cpusets Frederic Weisbecker
2012-03-21 13:58 ` [PATCH 25/32] x86: Exception " Frederic Weisbecker
2012-03-21 13:58 ` [PATCH 26/32] x86: Add adaptive tickless hooks on do_notify_resume() Frederic Weisbecker
2012-03-21 13:58 ` [PATCH 27/32] nohz: Don't restart the tick before scheduling to idle Frederic Weisbecker
2012-03-21 13:58 ` [PATCH 28/32] rcu: New rcu_user_enter() and rcu_user_exit() APIs Frederic Weisbecker
2012-03-21 13:58 ` [PATCH 29/32] rcu: New rcu_user_enter_irq() and rcu_user_exit_irq() APIs Frederic Weisbecker
2012-03-21 13:58 ` [PATCH 30/32] rcu: Switch to extended quiescent state in userspace from nohz cpuset Frederic Weisbecker
2012-03-21 13:58 ` [PATCH 31/32] nohz: Exit RCU idle mode when we schedule before resuming userspace Frederic Weisbecker
2012-03-21 13:58 ` [PATCH 32/32] nohz/cpuset: Disable under some configs Frederic Weisbecker
2012-03-27 15:02 ` [RFC][PATCH 00/32] Nohz cpusets v2 (adaptive tickless kernel) Gilad Ben-Yossef
2012-03-27 15:04 ` Gilad Ben-Yossef
2012-03-27 15:05 ` Gilad Ben-Yossef
2012-03-27 16:22 ` Christoph Lameter
2012-03-28 6:47 ` Gilad Ben-Yossef
2012-03-27 15:10 ` Peter Zijlstra
2012-03-27 15:18 ` Gilad Ben-Yossef
2012-05-22 21:31 ` Thomas Gleixner
2012-05-22 21:50 ` Steven Rostedt
2012-05-22 22:22 ` Thomas Gleixner
2012-03-28 11:43 ` Frederic Weisbecker
2012-03-30 0:33 ` Kevin Hilman
2012-03-30 0:45 ` Frederic Weisbecker
2012-03-30 2:07 ` Geoff Levand
2012-03-30 14:10 ` Kevin Hilman
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