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

[Paolo Bonzini]

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;
 }

> +/* 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?

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

Paolo