linux-kernel - Re: [RFC PATCH] use acpi_idle_enter_simple if bm_check && !.bm

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Date:	Mon, 19 Apr 2010 18:47:37 +0100
From:	Matthew Garrett <mjg59@...f.ucam.org>
To:	Luming Yu <luming.yu@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, Len Brown <lenb@...nel.org>,
	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	Arjan van de Ven <arjan@...ux.intel.com>
Subject: Re: [RFC PATCH] use acpi_idle_enter_simple if bm_check &&
	!.bm_control

On Tue, Nov 10, 2009 at 02:12:41PM +0800, Luming Yu wrote:

> I came across acpi processor idle driver, noticed that we can cut a
> bit overhead at C3 entry that can improve C3 residency a bit,
> especially when it has similar kernel config as old RHEL 5 kernel
> (2.6.18) on systems with as many as 64 logical CPUs. The point of this
> patch is bm_sts is an optional bit. It never returns 1 on systems with
> bm_check && !bm_control I tested. Instead, I have observed lower C3
> residency due to accessing bm_sts and relevant code on a system with
> 64 logical CPUs with HZ=1000. Please review. If make sense, please
> apply.

Saves 40W or so on a dual-socket Nehalem system here. Is there a reason 
it wasn't picked up?

-- 
Matthew Garrett | mjg59@...f.ucam.org
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