On Thu, 1 Nov 2018 at 04:02, Junaid Shahid <junaids@xxxxxxxxxx> wrote: > > On 10/30/2018 06:50 PM, Wanpeng Li wrote: > > > > If your "brownout period" is the time between previous get_dirty_log > > and next get_dirty_log and the "blackout" is get_dirty_log? > > > > No, the brownout period is the time during migration when the VM is still running on the source host. It will usually span multiple rounds of get_dirty_log calls and RAM transfers to the target host. The blackout period is when the VM completely stops running and includes one last get_dirty_log call to get the remaining pages. So the issue here is the same when I enable EPT D bit dirty log for Haswell 4 years ago, qemu will hold the BQL qemu_mutex_lock_iothread for every rounds of get_dirty_log calls, that's why I didn't observe real benefit when comparing to write protect at that time. Btw, why D bit dirty log is worse in blackout period? Regards, Wanpeng Li