[Qemu-devel] Block Migration and CPU throttling

[Peter Lieven]

Hi,

I just noticed that CPU throttling and Block Migration don't work together very 
well.
During block migration the throttling heuristic detects that we obviously make 
no progress
in ram transfer. But the reason is the running block migration and not a too 
high dirty pages rate.

The result is that any VM is throttled by 99% during block migration.

I wonder what the best way would be fix this. I came up with the following 
ideas so far:

- disable throttling while block migration is in bulk stage
- check if absolute number of num_dirty_pages_period crosses a threshold and 
not if its just
  greater than 50% of transferred bytes
- check if migration_dirty_pages > 0. This slows down throttling, but does not 
avoid it completely.

Peter