linux-kernel - Re: [PATCH 1/4] nohz: Force boot CPU outside full dynticks range

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Message-ID: <20130328073849.GA24433@gmail.com>
Date:	Thu, 28 Mar 2013 08:38:49 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Chris Metcalf <cmetcalf@...era.com>,
	Christoph Lameter <cl@...ux.com>,
	Geoff Levand <geoff@...radead.org>,
	Gilad Ben Yossef <gilad@...yossef.com>,
	Hakan Akkan <hakanakkan@...il.com>,
	Kevin Hilman <khilman@...aro.org>,
	Li Zhong <zhong@...ux.vnet.ibm.com>,
	Namhyung Kim <namhyung.kim@....com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 1/4] nohz: Force boot CPU outside full dynticks range


* Frederic Weisbecker <fweisbec@...il.com> wrote:

> The timekeeping job must be able to run early on boot
> because there may be some pre-SMP (and thus pre-initcalls )
> components that rely on it. The IO-APIC is one such users
> as it tests the timer health by watching jiffies progression.

Btw., while I agree that a conservative mode is probably wise for bootup, 
that IO-APIC assumption could be fixed or even removed.

If the IO-APIC code wants to know whether an interrupt fired, it can take 
a look at the kstat_irqs numbers?

Also, could we restrict the boot CPU's mode only during the early bootup 
stage - i.e. until we are ready to execute user-space init?

Thaks,

	Ingo
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