linux-kernel - Re: 2.6.20-rc6-mm3

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Message-Id: <1170796999.3455.43.camel@dwalker1>
Date:	Tue, 06 Feb 2007 13:23:19 -0800
From:	Daniel Walker <dwalker@...sta.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...l.org>, linux-kernel@...r.kernel.org
Subject: Re: 2.6.20-rc6-mm3

On Tue, 2007-02-06 at 22:09 +0100, Ingo Molnar wrote:
> * Daniel Walker <dwalker@...sta.com> wrote:
> 
> > > it's quite easy to explain: because of the new dynticks feature. 
> > > Both 'timer' and 'LOC' counts go way down.
> > 
> > I don't have that enabled tho .. This is with HRT/dynamic tick both 
> > off..
> 
> your kernel utilizes the kernelin a more optimal way: the new 
> clockevents code now utilizes the local APIC timer irq (represented by 
> the LOC field) for periodic interrupts. The local APIC timer irq has a 
> cost of ~2 usecs per IRQ, while the PIT irq is ~10 usecs per irq. With 
> HZ=1000 this means savings of ~8000 usecs per second - i.e. 8 msecs per 
> second, which is 0.8% more raw CPU power available - which isnt that 
> bad.

I'm happy it's better .. I'm not saying it's worse .

> we could make this clearer by renaming 'LOC' (which stands for 'LOCal 
> timer interupts' and was added [and misnamed] by yours truly many moons 
> ago) to 'apic-timer' and 'timer' to 'PIT-timer' but /that/ would be more 
> of a userspace visible change than the change in the counter rates.

If we change the current "timer" entry to be listed as "lapic-timer" and
not "IO-APIC-edge" (or one of the other names) and replace it with the
count from LOC , that would make sense cause that field already changes
depending if you have a io-apic or not ..

I think the regression (if you can call it that) is not scripts
crashing, but more people not know what's going on with there system .. 

Daniel

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