report revision 3 of the ACPI/SMBus PIIX4 controller
PATCH 1/1 report revision 3 of the ACPI/SMBus PIIX4 controller
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.
qemu/hw/acpi.c +1 -1
@@ -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
-------------------------------------------------------------------------
Check out the new SourceForge.net Marketplace.
It's the best place to buy or sell services for
just about anything Open Source.
http://ad.doubleclick.net/clk;164216239;13503038;w?http://sf.net/marketplace
Quoted 4 lines · Marcelo Tosatti
The PIIX4 ACPI controller prior to revision
0x3contains a bug where reading of the timer port is unreliable, so the kernel reads it three times for consistency check.
Quoted 10 lines
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.
Applied (to kvm's qemu), thanks.
Signature · 8 lines
error compiling committee.c: too many arguments to function ------------------------------------------------------------------------- Check out the new SourceForge.net Marketplace. It's the best place to buy or sell services for just about anything Open Source. http://ad.doubleclick.net/clk;164216239;13503038;w?http://sf.net/marketplace
Quoted 2 lines · Marcelo Tosatti
This reduces idle guest CPU consumption from 14% to 8% on 4-way KVM guest.
How do you get that high consumption? What combination of clocks/hz on host/guest are you using?
I am cursious, since my idle KVM process is at less than 1%.
Regards,
Anders.
-------------------------------------------------------------------------
Check out the new SourceForge.net Marketplace.
It's the best place to buy or sell services for
just about anything Open Source.
http://ad.doubleclick.net/clk;164216239;13503038;w?http://sf.net/marketplace
A message that is not in the archive (sent off-list or not yet received): [email protected]
Quoted 7 lines · Anders
Quoted 2 lines · Marcelo Tosatti
This reduces idle guest CPU consumption from 14% to 8% on 4-way KVM guest.
How do you get that high consumption? What combination of clocks/hz on host/guest are you using?
CONFIG_HZ=250
4-way SMP guest, 8-way Intel host (without the VMX TSC sync patch posted previously).
Quoted 1 line
I am cursious, since my idle KVM process is at less than 1%.
You have an UP guest right?
The problem is that the TSC synchronization check on boot is only performed on SMP guests. Intel hosts usually have their TSC synchronized, whereas AMD ones don't, so they fall back to use the ACPI PM timer (until the HPET QEMU/KVM support is in place).
UP guests use TSC as a clocksource by default, and TSC reads won't cause a VMExit.
-------------------------------------------------------------------------
Check out the new SourceForge.net Marketplace.
It's the best place to buy or sell services for
just about anything Open Source.
http://ad.doubleclick.net/clk;164216239;13503038;w?http://sf.net/marketplace
Quoted 1 line · Marcelo Tosatti
On Sun, Jan 13, 2008 at 12:19:20PM +0100, Anders wrote:
[...]
Quoted 4 lines
Quoted 2 lines
How do you get that high consumption? What combination of clocks/hz on host/guest are you using?
CONFIG_HZ=250
Okay, with nohz=off (in the guest) I also see some higher load. I didn't try the patch, though.
Quoted 2 lines
UP guests use TSC as a clocksource by default, and TSC reads won't cause a VMExit.
So for the lightest load (power saving), I should use UP and TSC?
Thanks,
Anders.
-------------------------------------------------------------------------
Check out the new SourceForge.net Marketplace.
It's the best place to buy or sell services for
just about anything Open Source.
http://ad.doubleclick.net/clk;164216239;13503038;w?http://sf.net/marketplace
A message that is not in the archive (sent off-list or not yet received): [email protected]
Quoted 11 lines · Anders
Quoted 1 line · Marcelo Tosatti
On Sun, Jan 13, 2008 at 12:19:20PM +0100, Anders wrote:
[...]
Quoted 4 lines
Quoted 2 lines
How do you get that high consumption? What combination of clocks/hz on host/guest are you using?
CONFIG_HZ=250
Quoted 7 lines
Okay, with nohz=off (in the guest) I also see some higher load. I didn't try the patch, though.
Quoted 2 lines
UP guests use TSC as a clocksource by default, and TSC reads won't cause a VMExit.
So for the lightest load (power saving), I should use UP and TSC?
Yes.
As you note NOHZ also helps dramatically.
-------------------------------------------------------------------------
Check out the new SourceForge.net Marketplace.
It's the best place to buy or sell services for
just about anything Open Source.
http://ad.doubleclick.net/clk;164216239;13503038;w?http://sf.net/marketplace