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Date: Thu, 07 Jun 2012 10:49:56 +0200
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Subject: Re: [Qemu-devel] [qemu-devel][RFC] Enable usb with default options
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To: Benjamin Herrenschmidt <benh@au1.ibm.com>
Cc: Hans de Goede <hdegoede@redhat.com>, Anthony Liguori <aliguori@us.ibm.com>, li zhang <zhlcindy@gmail.com>, qemu-devel@nongnu.org, zhlcindy@linux.vnet.ibm.com

Il 07/06/2012 10:40, Benjamin Herrenschmidt ha scritto:
> On Thu, 2012-06-07 at 10:32 +0200, Hans de Goede wrote:
>> Hi,
>>
>> Sorry for jumping in the middle of the thread, I missed the beginning
>> of this. Enabling USB by default, esp. emulating a USB mouse by default
>> is a *bad* idea. They way the periodic schedule of the various USB
>> controllers works means that emulating a USB device means a 1000 vm exits
>> per second extra, even when the vm is completely idle! USB powermanagement
>> can be used to negate this, but this is off in both Linux and Windows for
>> HID devices by default because there are too many broken HID devices.
> 
> On the other hand it is the only choice of input device on some
> platforms such as pseries (and MacG5 when I get to make it work :-)
> 
> Would it be possible to "whitelist" the QEMU emulated HID devices
> in the kernel to enable dynamic PM for them (at least when they sit
> alone on the bus) ? Or is our emulation busted too ?

At least in Fedora they are; from /usr/lib/udev/rules.d/42-usb-hid-pm.rules:

ACTION=="add", SUBSYSTEM=="usb", ATTR{product}=="QEMU USB Mouse", ATTR{serial}=="42", TEST=="power/control", ATTR{power/control}="auto"
ACTION=="add", SUBSYSTEM=="usb", ATTR{product}=="QEMU USB Tablet", ATTR{serial}=="42", TEST=="power/control", ATTR{power/control}="auto"
ACTION=="add", SUBSYSTEM=="usb", ATTR{product}=="QEMU USB Keyboard", ATTR{serial}=="42", TEST=="power/control", ATTR{power/control}="auto"

Paolo