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From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Christoph Lameter <cl@linux.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	Chris Metcalf <cmetcalf@mellanox.com>,
	Gilad Ben Yossef <giladb@mellanox.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ingo Molnar <mingo@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Rik van Riel <riel@redhat.com>, Tejun Heo <tj@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Viresh Kumar <viresh.kumar@linaro.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will.deacon@arm.com>,
	Andy Lutomirski <luto@amacapital.net>,
	Daniel Lezcano <daniel.lezcano@linaro.org>,
	linux-doc@vger.kernel.org, linux-api@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: clocksource_watchdog causing scheduling of timers every second (was [v13] support "task_isolation" mode)
Date: Thu, 11 Aug 2016 16:47:34 -0700	[thread overview]
Message-ID: <20160811234734.GJ3482@linux.vnet.ibm.com> (raw)
In-Reply-To: <alpine.DEB.2.20.1608111801320.8416@east.gentwo.org>

On Thu, Aug 11, 2016 at 06:02:34PM -0500, Christoph Lameter wrote:
> On Thu, 11 Aug 2016, Paul E. McKenney wrote:
> 
> > > With modern Intel we could run it on one CPU per package I think, but at
> > > the same time, too much in NOHZ_FULL assumes the TSC is indeed sane so
> > > it doesn't make sense to me to keep the watchdog running, when it
> > > triggers it would also have to kill all NOHZ_FULL stuff, which would
> > > probably bring the entire machine down..
> >
> > Well, you -could- force a very low priority CPU-bound task to run on
> > all nohz_full CPUs.  Not necessarily a good idea, but a relatively
> > non-intrusive response to that particular error condition.
> 
> Given that we want the cpu only to run the user task I would think that is
> not a good idea.

Heh!  The only really good idea is for clocks to be reliably in sync.

But if they go out of sync, what do you want to do instead?

							Thanx, Paul


  reply	other threads:[~2016-08-11 23:47 UTC|newest]

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-07-14 20:48 [PATCH v13 00/12] support "task_isolation" mode Chris Metcalf
2016-07-14 20:48 ` [PATCH v13 04/12] task_isolation: add initial support Chris Metcalf
2016-07-14 20:48 ` [PATCH v13 12/12] task_isolation: add user-settable notification signal Chris Metcalf
     [not found] ` <1468529299-27929-1-git-send-email-cmetcalf-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
2016-07-14 21:03   ` [PATCH v13 00/12] support "task_isolation" mode Andy Lutomirski
     [not found]     ` <CALCETrVddfd7ZDGpYs4CdkAMEmQCb6a-_5Um9bb4FO+XwWzOAA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2016-07-14 21:22       ` Chris Metcalf
2016-07-18 22:11         ` Andy Lutomirski
2016-07-18 22:50           ` Chris Metcalf
2016-07-18  0:42       ` Christoph Lameter
2016-07-21  2:04   ` Christoph Lameter
     [not found]     ` <alpine.DEB.2.20.1607202059180.25838-wcBtFHqTun5QOdAKl3ChDw@public.gmane.org>
2016-07-21 14:06       ` Chris Metcalf
2016-07-22  2:20         ` Christoph Lameter
2016-07-22 12:50           ` Chris Metcalf
2016-07-25 16:35             ` Christoph Lameter
     [not found]               ` <alpine.DEB.2.20.1607251133450.25354-wcBtFHqTun5QOdAKl3ChDw@public.gmane.org>
2016-07-27 13:55                 ` clocksource_watchdog causing scheduling of timers every second (was [v13] support "task_isolation" mode) Christoph Lameter
2016-07-27 14:12                   ` Chris Metcalf
     [not found]                     ` <f8d72e47-7e84-cbd0-869f-69bf452a8bfb-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
2016-07-27 15:23                       ` Christoph Lameter
     [not found]                         ` <alpine.DEB.2.20.1607271022130.25729-wcBtFHqTun5QOdAKl3ChDw@public.gmane.org>
2016-07-27 15:31                           ` Christoph Lameter
2016-07-27 17:06                             ` Chris Metcalf
2016-07-27 18:56                               ` Christoph Lameter
2016-07-27 19:49                                 ` Chris Metcalf
2016-07-27 19:53                                   ` Christoph Lameter
2016-07-27 19:58                                     ` Chris Metcalf
     [not found]                                       ` <2fefa17d-37c6-9669-724e-9ee0d841e7b2-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
2016-07-29 18:31                                         ` Francis Giraldeau
     [not found]                                           ` <CAC6yHM4LON5ASooVa_eUaDYsN1W0HYTMX76yHDxf8Mff0mKqiA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2016-07-29 21:04                                             ` Chris Metcalf
2016-08-10 22:16                   ` Frederic Weisbecker
2016-08-10 22:26                     ` Chris Metcalf
2016-08-11  8:40                     ` Peter Zijlstra
2016-08-11 11:58                       ` Frederic Weisbecker
2016-08-15 15:03                         ` Chris Metcalf
2016-08-11 16:00                       ` Paul E. McKenney
2016-08-11 23:02                         ` Christoph Lameter
2016-08-11 23:47                           ` Paul E. McKenney [this message]
2016-08-12 14:23                             ` Christoph Lameter
     [not found]                               ` <alpine.DEB.2.20.1608120922450.20310-wcBtFHqTun5QOdAKl3ChDw@public.gmane.org>
2016-08-12 14:26                                 ` Frederic Weisbecker
2016-08-12 16:19                                   ` Paul E. McKenney
     [not found]                                     ` <20160812161919.GV3482-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>
2016-08-13 15:39                                       ` Frederic Weisbecker
2016-08-11  8:27             ` [PATCH v13 00/12] support "task_isolation" mode Peter Zijlstra
2016-07-27 14:01 ` Christoph Lameter

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