linux-kernel - Re: [PATCH] arch/tile: new multi-core architecture for Linux

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Message-Id: <201005261909.03315.arnd@arndb.de>
Date:	Wed, 26 May 2010 19:09:02 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Chris Metcalf <cmetcalf@...era.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] arch/tile: new multi-core architecture for Linux

On Wednesday 26 May 2010 18:22:33 Chris Metcalf wrote:
> On 5/25/2010 4:12 PM, Thomas Gleixner wrote:
> > +unsigned long long sched_clock(void)
> > +{
> > +     u64 cycles;
> > +     u32 cyc_hi, cyc_lo;
> > +
> > +     if (unlikely(cyc2ns_mult == 0))
> > +             setup_clock();
> >
> >   Please initialize stuff before it is called the first time and not
> >   at some arbitrary point conditionally in a hotpath.
> >   
> 
> Looking more closely at this, the reason for this lazy initialization
> was that sched_clock() can be called from lockdep_init(), which runs way
> before any tasteful architecture-specific initialization can happen. 
> Perhaps the correct model is that during the early stages of boot, we
> are happy to shift by zero, multiply by zero, and claim the time is zero :-)

Yes, that is what other architectures do. The time remains zero during
early boot. setup_arch is probably a good place to start the clock.

	Arnd
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