On Tue, Jun 08, 2021 at 08:36:23PM +0100, Dr. David Alan Gilbert wrote: > * Peter Xu (pet...@redhat.com) wrote: > > On Tue, Jun 08, 2021 at 07:49:56PM +0100, Dr. David Alan Gilbert wrote: > > > * Peter Xu (pet...@redhat.com) wrote: > > > > These two commands are missing when adding the QMP sister commands. > > > > Add them, > > > > so developers can play with them easier. > > > > > > > > Cc: Dr. David Alan Gilbert <dgilb...@redhat.com> > > > > Cc: Juan Quintela <quint...@redhat.com> > > > > Cc: Leonardo Bras Soares Passos <lsoar...@redhat.com> > > > > Cc: Chuan Zheng <zhengch...@huawei.com> > > > > Cc: huang...@chinatelecom.cn > > > > Signed-off-by: Peter Xu <pet...@redhat.com> > > > > > > Reviewed-by: Dr. David Alan Gilbert <dgilb...@redhat.com> > > > > > > > --- > > > > PS: I really doubt whether this is working as expected... I ran one > > > > 200MB/s > > > > workload inside, what I measured is 20MB/s with current algorithm... > > > > Sampling > > > > 512 pages out of 1G mem is not wise enough I guess, especially that > > > > assumes > > > > dirty workload is spread across the memories while it's normally not > > > > the case.. > > > > > > What size of address space did you dirty - was it 20MB? > > > > IIRC it was either 200M or 500M, based on a 1G small VM. > > What was your sample time ?
10 seconds; I used the same sample time for below runs: https://lore.kernel.org/qemu-devel/YMEFqfYZVhsinNN+@t490s/ A large sample time does make dirty rate less indeed, as the same dirty page could be written again as 1 single page dirtyed in the host (while it's counted twice in the guest dirty workload). This effect should happen too if we further extend calc_dirty_rate with KVM_GET_DIRTY_LOG in the future as the 3rd method besides dirty ring. >From that pov, dirty ring is easier to be more "accurate" (I don't know whether it's suitable to say it's accurate; it's just easier to trap cases like writting to same page multiple times within a period), as the ring size is normally very limited (e.g. 4096 pages per vcpu), so even the guest workload writes the same page twice, as long as there's a ring collect between the two writes, they'll be counted twice too (each collect will reprotect the pages). -- Peter Xu
