From: Marcelo Tosatti <marcelo-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org>
To: kvm-devel <kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org>
Cc: qemu-devel-qX2TKyscuCcdnm+yROfE0A@public.gmane.org
Subject: [PATCH] report revision 3 of the ACPI/SMBus PIIX4 controller
Date: Fri, 11 Jan 2008 19:26:55 -0200 [thread overview]
Message-ID: <20080111212655.GA28753@dmt> (raw)
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
-------------------------------------------------------------------------
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WARNING: multiple messages have this Message-ID (diff)
From: Marcelo Tosatti <marcelo@kvack.org>
To: kvm-devel <kvm-devel@lists.sourceforge.net>
Cc: qemu-devel@nongnu.org
Subject: [Qemu-devel] [PATCH] report revision 3 of the ACPI/SMBus PIIX4 controller
Date: Fri, 11 Jan 2008 19:26:55 -0200 [thread overview]
Message-ID: <20080111212655.GA28753@dmt> (raw)
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
next reply other threads:[~2008-01-11 21:26 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-01-11 21:26 Marcelo Tosatti [this message]
2008-01-11 21:26 ` [Qemu-devel] [PATCH] report revision 3 of the ACPI/SMBus PIIX4 controller Marcelo Tosatti
2008-01-13 10:25 ` Avi Kivity
2008-01-13 10:25 ` [Qemu-devel] Re: [kvm-devel] " Avi Kivity
2008-01-13 11:19 ` Anders
[not found] ` <87ve5yynuv.fsf-MhEMtRviUwpApvB0Y80ENH9LOBIZ5rWg@public.gmane.org>
2008-01-13 14:22 ` Marcelo Tosatti
2008-01-13 15:49 ` Anders
[not found] ` <878x2tzpx4.fsf-MhEMtRviUwpApvB0Y80ENH9LOBIZ5rWg@public.gmane.org>
2008-01-14 13:24 ` Marcelo Tosatti
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