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

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Date:	Fri, 24 Oct 2008 14:05:44 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Pavel Machek <pavel@...e.cz>
Cc:	Mike Travis <travis@....com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jack Steiner <steiner@....com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Richard Purdie <rpurdie@...ys.net>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] SGI X86 UV: Provide a System Activity Indicator
	driver


* Pavel Machek <pavel@...e.cz> wrote:

> On Fri 2008-10-24 04:19:04, Mike Travis wrote:
> > [Ingo - could you let me know what's holding up this driver?
> > Thanks!, Mike]
> 
> I thought that...
> 
>  > +static __init void uv_scir_register_cpu_notifier(void)
> > +{
> > +	hotcpu_notifier(uv_scir_cpu_notify, 0);
> > +	idle_notifier_register(&uv_idle_notifier);
> > +}
> 
> ...Ingo said that idle_notifier_register is deprecated and going away?

yes, but i suspect Mike noticed that i acked Len's use of idle notifiers 
in the ACPI tree, and now he wants to refresh this discussion?

i cannot really believe why anyone would want to slow down the from-idle 
hotpath in such a lame way:

+       } else if (action == IDLE_END) {
+
+               uv_hub_info->scir.state |= SCIR_CPU_ACTIVITY;
+               uv_hub_info->scir.idle_off += elapsed;
+               uv_hub_info->scir.last = jiffies;
+       }

with such a lame and low-res timestamp:

+       unsigned long elapsed = jiffies - uv_hub_info->scir.last;

it's an absolutely pointless act of adding overhead. Just use a regular 
timer mechanism to update uv_hub_info->scir.idle_off.

	Ingo
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