Re: [Qemu-devel] [PATCH v7 3/3] Force auto-convegence of live migration

[Chegu Vinod <chegu_vinod@hp.com>]

On 6/24/2013 6:01 AM, Paolo Bonzini wrote:
> One nit and one question:
>
> Il 23/06/2013 22:11, Chegu Vinod ha scritto:
>> @@ -404,6 +413,23 @@ static void migration_bitmap_sync(void)
>>   
>>       /* more than 1 second = 1000 millisecons */
>>       if (end_time > start_time + 1000) {
>> +        if (migrate_auto_converge()) {
>> +            /* The following detection logic can be refined later. For now:
>> +               Check to see if the dirtied bytes is 50% more than the approx.
>> +               amount of bytes that just got transferred since the last time we
>> +               were in this routine. If that happens >N times (for now N==4)
>> +               we turn on the throttle down logic */
>> +            bytes_xfer_now = ram_bytes_transferred();
>> +            if (s->dirty_pages_rate &&
>> +               (num_dirty_pages_period * TARGET_PAGE_SIZE >
>> +                   (bytes_xfer_now - bytes_xfer_prev)/2) &&
>> +               (dirty_rate_high_cnt++ > 4)) {
>> +                    trace_migration_throttle();
>> +                    mig_throttle_on = true;
>> +                    dirty_rate_high_cnt = 0;
>> +             }
>> +             bytes_xfer_prev = bytes_xfer_now;
>> +        }
>
> Missing:
>
>   else {
>       mig_throttle_on = false;
>   }

Ok.
>> +/* Stub function that's gets run on the vcpu when its brought out of the
>> +   VM to run inside qemu via async_run_on_cpu()*/
>> +static void mig_sleep_cpu(void *opq)
>> +{
>> +    qemu_mutex_unlock_iothread();
>> +    g_usleep(30*1000);
>> +    qemu_mutex_lock_iothread();
>> +}
>> +
>> +    /* If it has been more than 40 ms since the last time the guest
>> +     * was throttled then do it again.
>> +     */
>> +    if (40 < (t1-t0)/1000000) {
> You're stealing 75% of the CPU time, isn't that a lot?

Depends on the dirty rate vs. transfer rate... I had tried 50% too and 
it took much longer for the migration to converge.

Vinod

>
>> +        mig_throttle_guest_down();
>> +        t0 = t1;
>> +    }
>> +}
>>
> Paolo
>
> .
>