linux-kernel - Re: udelay function delays the wrong time interval in multiprocessor system, if ARCH_HAS_READ_CURRENT_TIMER is not defined and on current timer is used.

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Message-ID: <CAM16m2n_Of0MJNtUsrL0MS2cXBZUHg9RzjSHcboDiHKB3s0cdw@mail.gmail.com>
Date:	Sat, 16 Mar 2013 11:32:43 +0800
From:	chpoph <chpoph@...il.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Nicolas Pitre <nico@...aro.org>,
	Liviu Dudau <Liviu.Dudau@....com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	will.deacon@....com
Subject: Re: udelay function delays the wrong time interval in multiprocessor
 system, if ARCH_HAS_READ_CURRENT_TIMER is not defined and on current timer is used.

On Sat, Mar 16, 2013 at 2:14 AM, Russell King - ARM Linux
<linux@....linux.org.uk> wrote:
> We don't support different CPUs running at different frequencies with
> the delay loop.  Sorry.

Does it means that a timer-based delay implementation must be used to
get an accurate delay in SMP. I think it should print a warning
message if the CPU delay loop is used in SMP.  In my system, the wrong
delay interval fluctuated with CPU frequencies caused a control
problem.
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