linux-kernel - Re: [RFC 0/4] Using HPET in MSI mode and setting up per CPU HPET timers

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Date:	Sat, 6 Sep 2008 14:42:34 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	venkatesh.pallipadi@...el.com
Cc:	tglx@...utronix.de, hpa@...or.com, linux-kernel@...r.kernel.org,
	shaohua.li@...el.com, Yinghai Lu <yhlu.kernel@...il.com>
Subject: Re: [RFC 0/4] Using HPET in MSI mode and setting up per CPU HPET
	timers


* venkatesh.pallipadi@...el.com <venkatesh.pallipadi@...el.com> wrote:

> Patchset that uses HPET timers in MSI mode (when supported) and sets 
> up per CPU HPET timers. This removes the dependency on IRQ0 timer 
> broadcast with LAPIC stopping in deep C-state, on platforms that 
> support HPET MSI mode.
> 
> On my test system with dual core CPU, the number of timer related 
> interrupts (HPET_MSI + IRQ0 + LAPIC) comes down from 180 to 95 over a 
> period of 10s, with these patches. This is on an idle system with 
> tickless enabled and when system is idle.
> 
> Patches against tip.

cool stuff!

this is _really_ how a modern dynticks system should look like on x86 - 
proper per CPU hardware timers that are southbridge based.

There's a few routine checks this new has to pass: we've got to see how 
widely this works and whether there are any bugs/quirks to take care of, 
so i created a separate feature topic for it: tip/timers/hpet-percpu.

This tip/timers/hpet-percpu feature topic tree is based on irq/sparseirq 
+ timers/hpet + timers/urgent - which had some changes in the hpet area. 
I merged up the conflicts - please double check the result. I also did 
cleanups for a few style problems that were present in hpet.c.

I've merged it into tip/master as well and will run a few tests before 
pushing it out.

	Ingo
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