[libvirt] [ROC] migration: set cpu throttle value by workload

Hi all, When migrating a guest which consumes too much CPU & memory, dirty pages amount will increase significantly, so does the migration time, migration can not even complete, at worst. So I made an RFC patch in QEMU to set cpu throttle value by workload when migration. The test result and the RFC patch are here: https://lists.gnu.org/archive/html/qemu-devel/2017-01/msg03479.html But this idea was not accepted by QEMU community. So I want to do a similar feature in libvirt: Step 1: Add --auto-converge-smart parameter to migrate. Step 2: Add a timer in qemu-driver to get the 'info migrate' to check if the dirty-pages-rate updated every 1 second or 0.5 second when migration. Step 3: If updated, change the cpu throttle value according to the dirty-pages-rate and page-size by 'migrate_set_parameter cpu-throttle-increment' I think this feature makes auto-converge smarter than leaving the cpu throttle value with default 20/10 or set by users. And also it can save time. Any comments will be welcome. Thanks, Chao Fan