linux-kernel - Re: [PATCH 1/1] SGI X86 UV: Provide a System Activity Indicator driver

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Date:	Thu, 02 Oct 2008 07:33:44 -0700
From:	Mike Travis <travis@....com>
To:	Pavel Machek <pavel@...e.cz>
CC:	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>, rpurdie@...ys.net,
	Jack Steiner <steiner@....com>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 1/1] SGI X86 UV: Provide a System Activity Indicator	driver

Pavel Machek wrote:
>> Pavel Machek wrote:
>>>> Another relevant point is that I will be adding a bit more functionality
>>>> to disable the timer interrupt on truly "idle" cpus (like have been idle
>>>> for some amount of seconds).  We would then use the "exit from idle"
>>>> callback to reestablish the timer interrupt.  [This would allow them to
>>>> enter power down states if appropriate.]
>>> Should you look at nohz instead of reinventing it? 
>> Thanks, I did look at it.  Quite complex.  Maybe I'm missing something
>> but I don't see how it fits in?  Are you saying I should be using
> 
> I seen your remark above about disabling timer interrupt on idle
> cpus. That's exactly nohz functionality, right? Maybe I misunderstood
> you and you meant "my monitoring interrupt" and not "generic system
> timer interrupt"?
> 
> 									Pavel

Ahh, yes, now I see... ;-)

And thanks for the pointer, I hadn't looked at this before.

In regards to "powering down" a UV system, it's not clear yet that it will
help much unless we can power down a whole lot more of the system than just
the cpus... ;-)  [but in reality, reducing power use any time you can is 
real necessity.]

Btw, are you ok with the remainder of the patch?

Thanks,
Mike
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