* Yang Hongyang (yanghongy...@huawei.com) wrote: > > > On 2017/4/24 20:06, Juan Quintela wrote: > > Yang Hongyang <yanghongy...@huawei.com> wrote: > >> Hi all, > >> > >> We found dirty log switch costs more then 13 seconds while migrating > >> a 4T memory guest, and dirty log switch is currently protected by QEMU > >> BQL. This causes guest freeze for a long time when switching dirty log on, > >> and the migration downtime is unacceptable. > >> Are there any chance to optimize the time cost for dirty log switch > >> operation? > >> Or move the time consuming operation out of the QEMU BQL? > > > > Hi > > > > Could you specify what do you mean by dirty log switch? > > The one inside kvm? > > The merge between kvm one and migration bitmap? > > The call of the following functions: > memory_global_dirty_log_start/stop();
I suppose there's a few questions; a) Do we actually need the BQL - and if so why b) What actually takes 13s? It's probably worth figuring out where it goes, the whole bitmap is only 1GB isn't it even on a 4TB machine, and even the simplest way to fill that takes way less than 13s. Dave > > > > > Thanks, Juan. > > > > -- > Thanks, > Yang -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
