linux-kernel - Re: Clockevents: one-shoot mode is never enabled if local apic timer is disabled

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Message-Id: <200704021323.45585.maximlevitsky@gmail.com>
Date:	Mon, 2 Apr 2007 13:23:45 +0300
From:	Maxim Levitsky <maximlevitsky@...il.com>
To:	tglx@...utronix.de
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Clockevents: one-shoot mode is never enabled if local apic timer is disabled

On Monday 02 April 2007 12:34:44 Thomas Gleixner wrote:
> Maxim,
> 
> can you please fix your mail client to do proper line wraps at 78
> chars ?
Sure, but this way it mangles patches :-)
> 
> On Mon, 2007-04-02 at 11:57 +0300, Maxim Levitsky wrote:
> > Hi,
> > 
> > I finally figured out why one-shoot mode is enabled on my system only
> > and only if local apic is enabled.
> 
> You could have asked me :)
Thanks
> 
> > I tried to remove this check and this resulted in hard lock-up during
> > boot with nolapic_timer
> > Maybe this was connected to the fact that this function is called on
> > both cpus, and if one set a 
> > broadcasting device(HPET) to one shoot mode, second is still not aware
> > of this.
> > 
> > Is it a bug or feature ?
> 
> One shot mode - used for NO_HZ and HIGH_RES - requires a working per cpu
> timer.
> 
> When you disable the lapic timers, then we register the lapic timers
> just as dummy devices to utilize the broadcast mechanism. Otherwise the
> second CPU would be not working at all. I decided not to enable
> nohz/highres when we have no usable per cpu devices available. 
> 
> So consider it a feature :)
> 
> 	tglx
> 
> 
> 
Hi, 

Fortunately on my system lapic timer works.
But then tick_broadcast_switch_to_oneshot is redundant, isn't it? 

Thanks for quick answer,
	Best regards,
		Maxim Levitsky

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