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From: | Anthony Liguori |
Subject: | Re: [Qemu-devel] [5056] add DisplayState->idle (Samuel Thibault) |
Date: | Thu, 21 Aug 2008 20:24:11 -0500 |
User-agent: | Thunderbird 2.0.0.16 (X11/20080723) |
Paul Brook wrote:
On Thursday 21 August 2008, Anthony Liguori wrote:Revision: 5056 http://svn.sv.gnu.org/viewvc/?view=rev&root=qemu&revision=5056 Author: aliguori Date: 2008-08-21 20:08:55 +0000 (Thu, 21 Aug 2008) Log Message: ----------- add DisplayState->idle (Samuel Thibault)This really needs a comment saying exactly what this field means.
Fair enough. Gerd or Samuel, can you send a patch?
I'm guessing it's set by the GUI routines to tell the emulated device that it doesn't need to update the display.
Yes, that's what it does AFAIUI.
Currently the GUI has to poll the emulated device to get updated output, which means this flag is the exact opposite of what I'd intuitively expect.
The Xen PV frame buffer is a little different than the other devices we emulate. The Linux driver provides a linear framebuffer to userspace via the fbdev interface. There is no update interface for fbdev though so it periodically zaps the page table mappings in order to do dirty tracking which it then uses to send the host update regions. Presumably, this idle flag is actually communicated to the guest to let it know that it does not need to do dirty tracking for the time being. Presumably, this has an observable performance advantage. I believe the refresh rate is pretty high within the guest so I can imagine this being significant when using guests with CONFIG_NO_HZ.
Regards, Anthony Liguori
Paul
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