Il 04/02/2014 13:16, Alexey Kardashevskiy ha scritto:
On 02/04/2014 11:07 PM, Paolo Bonzini wrote:
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.
Make a patch? :)
I mean, my mistake. :) I assumed 3000 ms = 3*10^9.
30 ms is too little, but 3000 ms is probably too much for a default.
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.
Well, it will fix it in my particular case but in a long run this does not
feel like a fix - there should be a way for migration_thread() to know that
ram_save_iterate() sent all dirty pages it had to send, no?
No, because new pages might be dirtied while ram_save_iterate() was running.
Paolo
