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Date: Thu, 31 Jan 2013 13:21:18 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: anish singh <anish198519851985@gmail.com>
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Subject: Re: [PATCH] printk: Avoid softlockups in console_unlock()
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On Thu, 31 Jan 2013 13:14:05 +0530
anish singh <anish198519851985@gmail.com> wrote:

> > If it does need ratelimiting, I'd worry about using jiffies for that.
> > If the kernel is spending a long time with interrupts disabled, jiffies
> > might not be incrementing.  Using the CPU timestamp would be better
> > (eg, sched_clock()).
> 
> http://lxr.free-electrons.com/source/kernel/sched/clock.c#L75
> I am puzzled because of this definition(above link).Sched_clock is
> dependent on jiffies and jiffies is blocked so how sched_clock would
> be better(I am 100% missing something very obvious)?
> 
> Is it that sched_clock is not dependent on jiffies?

yes, I think sched_clock is dependent on jiffies for some architectures.

I was really using sched_clock as a place-filler for "some timer which
keeps running when interrupts are disabled" ;) I'm not really sure what
that would be nowadays - even get_cycles() isn't implemented on some
architectures.  I guess some architectures will need a lame fallback or
some sort.