Re: [Qemu-devel] [libvirt-users] Adjust disk image migration (NBD)

[Joaquim Barrera]

On 24/02/14 23:26, Paolo Bonzini wrote:
> > Thanks for raising this.
> >
> > I noticed that mirror_run() does not throttle the first loop where it
> > populates the dirty bitmap using bdrv_is_allocated_above().
> This is on purpose.  Does it causes a noticeable stall in the guest?
>
> > The main
> > copy loop does take the speed limit into account but perhaps that's
> > broken too.
> Yeah, it looks broken.  Each iteration of the loop can write much more
> than sectors_per_chunk sectors, but here:
>
>              if (s->common.speed) {
>                  delay_ns = ratelimit_calculate_delay(&s->limit, 
> sectors_per_chunk);
>              } else {
>                  delay_ns = 0;
>              }
>
> the second argument is fixed. :/
>
> Paolo

Thanks for the answer. Something is still not clear to me. Are we in 
front of a bug (that means, something that could be fixed) or is this 
behaviour somehow expected for some reason? More and more tests I am 
doing, I get allways the same throughput chart: unlimited bandwidth when 
syncronizing the disk, and smooth bandwidth limit when migrating RAM.

Joaquim