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

[Paolo Bonzini]

Il 24/06/2013 15:08, Chegu Vinod ha scritto:
> 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.

Fair enough, thanks!

Paolo