Re: [Qemu-devel] migration: broken ram_save_pending

[Paolo Bonzini]

Il 04/02/2014 12:59, Alexey Kardashevskiy ha scritto:
> > > With the default throttling of 32 MiB/s, bandwidth must be something like
> > > 33000 (expressed in bytes/ms) with the default settings, and then max_size
> > > should be 33000*3*10^9 / 10^6 = 6000000.  Where is my computation wrong?
>
> migrate_max_downtime() = 30000000 = 3*10^7.

Oops, that's the mistake.

> When the migration is in iterating stage, bandwidth is a speed in last
> 100ms which is usually 5 blocks 250KB each so it is
> 1250000/100=12500bytes/s and max_size=12500*30000000/10^6=375000 which is
> less than the last chunk is.

Perhaps our default maximum downtime is too low.  30 ms doesn't seem 
achievable in practice with 32 MiB/s bandwidth.  Just making it 300 ms 
or so should fix your problem.

Paolo