linux-kernel - Re: [PATCH] clocksource: Avoid selecting mult values that might overflow when adjusted

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Message-ID: <20111110150521.GD29614@elte.hu>
Date:	Thu, 10 Nov 2011 16:05:21 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Yong Zhang <yong.zhang0@...il.com>
Cc:	John Stultz <john.stultz@...aro.org>,
	LKML <linux-kernel@...r.kernel.org>,
	David Daney <ddaney.cavm@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Chen Jie <chenj@...ote.com>, zhangfx <zhangfx@...ote.com>
Subject: Re: [PATCH] clocksource: Avoid selecting mult values that might
 overflow when adjusted


* Yong Zhang <yong.zhang0@...il.com> wrote:

> On Tue, Nov 08, 2011 at 01:39:02PM -0800, John Stultz wrote:
> > On Tue, 2011-11-08 at 13:02 +0800, Yong Zhang wrote:
> > > On Mon, Nov 07, 2011 at 07:09:00PM -0800, John Stultz wrote:
> > > > Yong: Can you also give this a test run to make sure you don't see any
> > > > problems?
> > > 
> > > Still get warning (3.2-rc1 + your patch):
> > > 
> > > [    0.017009] ------------[ cut here ]------------
> > > [    0.022156] WARNING: at /build/linux/kernel/time/timekeeping.c:828 do_timer+0x402/0x4e0()
> > > [    0.035917] Adjusting jiffies more then 11% (1024068096 vs 1024064000)
> > 
> > Ah. We're tripping the warning here in early boot. We use jiffies as the
> > default clocksource initially even before it is registered and the
> > maxadj is then set. So since its null here, any adjustment triggers the
> > warning.
> > 
> > That's easy enough to avoid. Can you give this updated version a try to
> > make sure I didn't miss anything else?
> 
> This version boot well on my side.
> 
> echo acpi_pm > /sys/devices/system/clocksource/clocksource0/current_clocksource
> echo hpet > /sys/devices/system/clocksource/clocksource0/current_clocksource
> 
> both work well.
> 
> Tested-by: Yong Zhang <yong.zhang0@...il.com>

John, mind sending a pull request for this, based against current 
tip:timers/core? I'm quite sure it will fix the boot warning i saw as 
well.

Thanks,

	Ingo
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