From: Frederic Weisbecker <frederic@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
Anna-Maria Gleixner <anna-maria@linutronix.de>,
Sebastian Siewior <bigeasy@linutronix.de>,
Paul McKenney <paulmck@linux.vnet.ibm.com>,
Peter Zijlstra <peterz@infradead.org>,
Frederic Weisbecker <fweisbec@gmail.com>,
Ingo Molnar <mingo@kernel.org>,
stable@vger.kernel.org
Subject: Re: [patch 2/4] nohz: Prevent erroneous tick stop invocations
Date: Tue, 26 Dec 2017 16:17:48 +0100 [thread overview]
Message-ID: <20171226151746.GA6560@lerouge> (raw)
In-Reply-To: <20171222145337.713295508@linutronix.de>
On Fri, Dec 22, 2017 at 03:51:13PM +0100, Thomas Gleixner wrote:
> The conditions in irq_exit() to invoke tick_nohz_irq_exit() are:
>
> if ((idle_cpu(cpu) && !need_resched()) || tick_nohz_full_cpu(cpu))
>
> This is too permissive in various aspects:
>
> 1) If need_resched() is set, then the tick cannot be stopped whether
> the CPU is idle or in nohz full mode.
That's not exactly true. In nohz full mode the tick is not restarted on the
switch from idle to a single task. And if an idle interrupt wakes up a
single task and enqueues a timer, we want that timer to be programmed even
though we have need_resched().
next prev parent reply other threads:[~2017-12-26 15:17 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20171222145111.919609918@linutronix.de>
2017-12-22 14:51 ` [patch 1/4] timer: Use deferrable base independent of base::nohz_active Thomas Gleixner
2017-12-25 16:24 ` Frederic Weisbecker
2017-12-22 14:51 ` [patch 2/4] nohz: Prevent erroneous tick stop invocations Thomas Gleixner
2017-12-26 15:17 ` Frederic Weisbecker [this message]
2017-12-27 18:22 ` Thomas Gleixner
2017-12-27 18:24 ` Thomas Gleixner
2017-12-27 20:58 ` Thomas Gleixner
2017-12-29 16:12 ` Frederic Weisbecker
2017-12-22 14:51 ` [patch 3/4] timer: Invoke timer_start_debug() where it makes sense Thomas Gleixner
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