From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43)
	id 1JDRP2-0003UZ-TK
	for qemu-devel@nongnu.org; Fri, 11 Jan 2008 16:27:00 -0500
Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43)
	id 1JDRP1-0003UN-G1
	for qemu-devel@nongnu.org; Fri, 11 Jan 2008 16:26:59 -0500
Received: from [199.232.76.173] (helo=monty-python.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1JDRP1-0003UK-B0
	for qemu-devel@nongnu.org; Fri, 11 Jan 2008 16:26:59 -0500
Received: from kanga.kvack.org ([66.96.29.28])
	by monty-python.gnu.org with esmtp (Exim 4.60)
	(envelope-from <marcelo@kvack.org>) id 1JDRP0-0002Eg-WE
	for qemu-devel@nongnu.org; Fri, 11 Jan 2008 16:26:59 -0500
Date: Fri, 11 Jan 2008 19:26:55 -0200
From: Marcelo Tosatti <marcelo@kvack.org>
Message-ID: <20080111212655.GA28753@dmt>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
Subject: [Qemu-devel] [PATCH] report revision 3 of the ACPI/SMBus PIIX4
	controller
Reply-To: qemu-devel@nongnu.org
List-Id: qemu-devel.nongnu.org
List-Unsubscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.gnu.org/pipermail/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: kvm-devel <kvm-devel@lists.sourceforge.net>
Cc: qemu-devel@nongnu.org


The PIIX4 ACPI controller prior to revision 0x3 contains a bug where
reading of the timer port is unreliable, so the kernel reads it three
times for consistency check.

QEMU does not suffer from that problem :)

The datasheet for PIIX4, PIIX4E, and PIIX4M is the same. I failed to
find any indication that the revision increase could affect anything
other than the PMTimer port read.

This reduces idle guest CPU consumption from 14% to 8% on 4-way KVM
guest.

--- kvm-userspace.orig/qemu/hw/acpi.c
+++ kvm-userspace/qemu/hw/acpi.c
@@ -486,7 +486,7 @@ i2c_bus *piix4_pm_init(PCIBus *bus, int
     pci_conf[0x03] = 0x71;
     pci_conf[0x06] = 0x80;
     pci_conf[0x07] = 0x02;
-    pci_conf[0x08] = 0x00; // revision number
+    pci_conf[0x08] = 0x03; // revision number
     pci_conf[0x09] = 0x00;
     pci_conf[0x0a] = 0x80; // other bridge device
     pci_conf[0x0b] = 0x06; // bridge device