[Qemu-devel] Re: [PATCH 09/10] Exit loop if we have been there too long

[Takuya Yoshikawa]

Thanks for the answers Avi, Juan,

Some FYI, (not about the bottleneck)

On Wed, 01 Dec 2010 14:35:57 +0200
Avi Kivity <address@hidden> wrote:

> > >   - how many dirty pages do we have to care?
> >
> > default values and assuming 1Gigabit ethernet for ourselves ~9.5MB of
> > dirty pages to have only 30ms of downtime.
> 
> 1Gb/s * 30ms = 100 MB/s * 30 ms = 3 MB.
> 

3MB / 4KB/page = 750 pages.

Then, KVM side processing is near the theoretical goal!

In my framebuffer test, I tested

  nr_dirty_pages/npages = 576/4096

case with the rate of 20 updates/s (1updates/50ms).

Using rmap optimization, write protection only took 46,718 tsc time.
Bitmap copy was not a problem of course.

The display was working anyway at this rate!


In my guess, within 1,000 dirty pages, kvm_vm_ioctl_get_dirty_log()
can be processed within 200us or so even for large RAM slot.
 - rmap optimization depends mainly on nr_dirty_pages but npages.

Avi, can you guess the property of O(1) write protection?
I want to test rmap optimization taking these issues into acount.



Of course, Kemari have to continue synchronization, and maybe see
more dirty pages. This will be a future task!


Thanks,
  Takuya